You're reading this guide because you want or need to buy a tool - even if you have lots and lots of them - for one of the following reasons: 1) You broke one, 2) You need it, or 3) Just Because (my personal favorite).  My experience in wrenching with Snap-On, Mac, Matco, Williams, Fleet, Ward's, Challenger, Blackhawk, KD, Proto, Allen, Husky, Craftsman, Stanley, no-name Chinese tools, no-name Japanese tools, and others may be of some use to you.  

Your first problem is figuring out how much to spend.  Your main crunch (if you've got one) would probably be more than happy if you didn't spend anything at all - there's too much crap in the garage already.  OK, let's just say it's always nice to spend less.  So how much less?

Probably the most important question is how often are you going to use this tool.  The guys whose livelihood depends on their tools will generally use Snap-On, Mac, or Matco; Craftsman, Proto and S-K also show up on a regular basis.  There is a reason for this - cheap tools have an annoying tendency to wear out and/or break (we'll talk about the breakage factor later).  For example, if you're going to use a 24mm socket on a daily basis, it makes more sense buying the best you can afford - the higher cost will even out because they will (usually) last longer. 

The second question is just how picky you are.  Those that buy cheap tools have never known the feeling of holding a great tool in your hand - it will be balanced, heavy, and Just Feel Right.  Holding (and using) a really good tool is roughly equivalent to caressing the metal equivalent of Claudia Schiffer. If you can get hold of an 18" Snap-On 1/2" drive breaker bar, you'll see what I mean. 

The third question is simply - are you going to use this tool to do something stupid?  As an example, back when I was young and stupid (instead of just young), one of my first wrenching experiences was changing out a drive axle in my first-generation Honda Civic.  Axle nuts are notoriously difficult to budge, and this one was no exception.  I finally put a three-foot-long piece of pipe over the ratchet handle, and slipped a six-foot-long length of fence post over that.  And jumped on it.  Had the socket and/or ratchet been anything less than the Williams items I was using, something would have broken (probably my head).  And if you break something, it's nice to have a warranty.  Craftsman, for example, can be easily changed out at any Sears store.  Don't be embarrassed, they're used to it, and the clerks won't interrogate you to see if you've been using that screwdriver as a pry bar.  Snap-On tools are easily exchanged (although you rarely hear of one breaking) and those trucks show up almost everywhere.   Many other brands have excellent - even lifetime - warranties, but just try getting it honored - you'll probably have to find the manufacturer and send it back, and I find that just more trouble than it's worth.

The fourth question is - is this tool safe from theft? Tools are even more prone than car keys to wander off when you're not looking, and the more expensive the tool, the more likely it is to wander.  You may not go as far as said in one Snap-On sticker ("Want to borrow a tool?  The last guy who borrowed one is in the bottom drawer"), but you'll probably want to have some sort of identification on your tools.

So what are you going to buy?  The first rule is - avoid cheap.  Period.  There is a reason you can buy a "complete socket wrench set" for $5 - it's built cheap from cheap materials.  Your first clue a tool is cheap is that it feels too light - experiment with holding, for example, a nice S-K 1/2" drive socket in one hand and one of those no-name sockets with thin chrome plate and a perfectly round little hole in the center in the other.  Feel how much heavier the S-K socket is?  Steel is expensive.  Many cheap tools are made of inexpensive alloys, apparently comprised equally of aluminum, wet newspapers and old tuna cans.

The second rule - looks aren't everything.  There are a LOT of tools out that that try to look expensive, even mimicking the look of some high-end brand (swap meet sellers of Snap-On lookalikes are notorious for this).  When in doubt, look for deep engraving or forged markings - the barely visible  stamped words or numbers (or complete lack thereof) on cheap tools can be a dead giveaway.  On the other hand, many old or well-used tools will have their markings worn off or originally possessed no markings whatsoever.  Use your judgment.

The third rule - never buy something that can hurt you.  If you live far from a tool vendor, a broken tool can render your whole weekend useless.  Or, more likely, you'll be putting serious torque on some tool, and it will either slip or break.  In either case, the end result to your hand (or head!) will look and sound roughly equivalent to dropping a ripe cantaloupe off a 10-foot stepladder.  Your knuckles are expensive.  So are teeth.  I was under my Olds 98 (yes, with that tufted velour cushion interior) many years ago, pulling down to remove a recalcitrant starter bolt, when the cheap Gedore wrench I was using rounded off the corners of the bolt and smacked into my face.  One split lip and a chipped front tooth later, it occurred to me that I had learned something. 

The fourth rule - forged over cast.  Cast anything breaks more easily, so cast tools will usually be fatter, clumsier and not as strong as their forged equivalents.  An example was when I was working on my late, lamented 450SL - my 40th birthday present to me.  Being cheap and/or broke, for years I refused to buy a new hydraulic fan clutch - the dealer price of almost $300 probably had something to do with it.  And you can buy a used one at your local Pic-n-Pull for about $10, which will usually last about a month.  Unfortunately, the 10mm bolts holding the fan clutch on were cleverly recessed.  Consequently, once the edges of the bolts were rounded enough that my cheap open-end wrench wouldn't grip, I tried using the box end.  No dice.  The cheap cast wrench I was using had a box end too thick to fit in the recess.  I was faced with the prospect of removing the radiator AND the condensor AND all the aassociated hoo-ha in the way in order to get the fan clutch off.  Earlier in my wrenching career I would have given up, and taken the car to the mechanic.  That time, I got smart - I went to the local hardware store and bought a nice "Master Mechanic" forged combination 10mm and 11mm box-end wrench for about eight bucks.  And guess what?  The box end, much thinner than the one on the cheap cast wrench, slipped neatly into the recess, grabbed the rounded bolt head slick as you please, and the job was done in a few minutes.

The fifth rule - balance your time versus your money.  If you can wait to get the tool, AND if you have the time to spend on hunting for it or them, hold out for good used tools vs. new cheap ones.  Ebay is a great resource for this.  A compromise, should you need the tool immediately, is buy Craftsman - they are generally well priced and almost always priceworthy.  If you need a tool to work first time, every time, spend as much as you can afford, you'll thank me later.

The sixth rule - they're cheaper by the dozen.  Almost always, you can buy a full set of whatever tools you want for less than the individual prices of each item included.  Once again, Snap-On is the exception to the rule here - there's no discount to buying them in bulk.  But if you buy a Craftsman set (to use an example), you'll pay as little as 50% - sometimes less - of the aggregate cost of buying the sets individually.  And make a habit of watching those Sears sale brochures that show up in your mail - buy 'em when they're on sale.

The seventh rule - it's fun to hunt on Ebay.  Keep track of what is selling, and use the "advanced search" to find what it typically sells for, and you'll be able to better predict what a good bid will be (and if you can afford it).  I've bought more than one tool on impulse (particularly in the "Collectibles" section), and several have turned out as favorites.

Finally, some random thoughts about various common brands, in no particular order -

Snap-On - the holy grail of automotive tools.  In quality and price, overall the highest.  You definitely get what you pay for here.  For example, Snap-On uses a process on their screwdriver tips that make them both highly accurate and virtually indestructible - if you have a screw with a damaged head, your best chance is a Snap-on screwdriver.  My favorite ratchet wrench is an old Snap-On "bull" wrench, with a bar handle much thicker and heavier than their usual style.    

Mac, Matco -  pretty much the same as Snap-On, but I don't like their screwdrivers as much.

Williams - also known as J.H. Williams - heavy, solid and virtually indestructible, Williams has been THE industrial-use tool maker of choice for over 75 years.  Williams is now, btw, a division of Snap-On, though I haven't seen any difference in the quality of the tools.  Williams "Superratchets" in the -52 and higher series have remarkably fine ratchet mechanisms - important if you're in a tight spot with very little wiggle room.   Earlier ones, while having coarser mechanisms, are great for heavy duty work.  A set of Williams SAE 1/2" drive sockets, with their accompanying ratchet, have been mine for over 25 years, and have never let me down.

Proto, S-K, Napa, New Britain, Allen, KD - Always reliable, never cheap.  S-K ratchets have too coarse a mechanism for my taste, try before you buy.  I have a suspicion that Allen and KD tools are made in the same factory; I have a pair of otherwise identical 24mm polished combination wrenches from those makers. 

Craftsman - I used to think that Craftsman was, bar none, the best value for money.  Lately, I'm not so sure.  A few years back, Craftsman changed manufacturers, and the newer stuff (compare your old Craftsman sockets to new ones, example) just doesn't seem to be of the same quality or to hold up as well, particularly Phillips-head screwdrivers and cutting tools.  The combination sets tend to include their really cheap ratchets, which are coarse, clunky and a pain in the ass.  I don't like their line of Companion tools at all.

Gedore - I've had several unhappy experiences with their wrenches - coarse, fat and sloppy.

Generic Taiwanese tools - in my experience, usually shoddy, sometimes excellent.  Don't prejudge, sometimes an excellent value for money.  The better ones will usually be stamped "chrome vanadium".

Generic (mainland) Chinese tools - see above. 

Husky and Stanley - a notch or two below the run-of-the-mill Craftsman stuff. 

Generic tools trying to look expensive - don't bother.  Ever.

Happy wrenching!