Over the years, many times I have been asked  "What is the best diamond saw blade for cutting...". Blades are a lot like cars, some are made really well and cost a small fortune, others are really so-so and are very inexpensive.
But knowing how to care for any blade will make either blade better.

There are some simple guidelines you should know about cutting rocks with diamond.
First is that diamond will cut through everything. Sometimes though, not as well as you'd like because the blade "loads" up or becomes dull.
 Having a dressing stick  around,  designed to clean off and expose fresh cutting diamond is a good idea, they are cheap compared to blades and last much longer too so will service your blades for a long time.
Choose the blade for the job! You don't want to use a tile or concrete saw, with kerfs of up to 0.125 inch on a 5 carat sized piece of rough opal. You'd loose half the stone just cutting it!
Likewise, you wouldn't use a blade with a copper core and kerf of 0.009 inch on a 3 inch thick piece of picture chert or jasper. These are hard stones with zones of varying densities which will push and pull the blade into directions and result in the most convoluted cuts you'll ever see and most likely ruin the blade in the process.

You also do not want to use a tile or concrete blade on facet rough, especially if the blade has those cooling notches in the rim. These will catch on the rough, and throw it against the far wall, shatter a great piece.

Choosing blades should be aimed at the types of rock you will be cutting. Slab blades are generally thick and very stiff to cut the hard cherts, agates, and petrified wood slabs so enjoyed by hobbiests as a starting point for cabs. These materials are inexpensive and loosing an 1/8th of an inch or more to the cut itself isn't a big loss.
Opals on the otherhand tend to be pricey and so loss of material while cutting can be expensive. Using very thin blades with a small kerf (a 0.006 blade typically has a 0.009 kerf and adding a couple points you can figure a 0.012 inch cutting loss for blade wobble and general cutting from excess material traveling with the blade) on opals and fine facet rough saves expensive material. And unless you are equiped with the proper tools to cleave stones (which doesn't work on opals), you are going to have sawing losses.

You have to use a coolant with diamonds (many concrete saws are designed to be dry cutting, but we're not talking concrete or tiles here) which saves the blade and the stone in the case of opals or fragile facet material like tourmaline. If your worried about a mess, do it outside, but use water or cutting oils or you'll be wanting to invest in a blade manufacturer.

Sometimes you can rationalize a general purpose blade of moderate thickness and a good stiff core for most of your work. These blades often become the mainstay of your cutting work and will do you fine. They don't deflect easily, they have a good amount of diamond for cutting and they are fairly inexpensive. Don't cut tiles or concrete with them. Do use lots of coolant.
Make sure you have a good amount of diamond bonded to the rim. Those with a 1/4 inch of diamond bonding to the side of the blade may only have half the diamond of one with a 1/16 of an inch zone per inch of blade edge. Looks can mislead you This doesn't mean the one with 1/16 of an inch of bonded or embedded diamond is better. But it points out that once you chooce a thickness, check the diamond cutting surface (this is what your really after anyway) and read up on the different manufacturers and the process they use to make their blades.
Steel cores aren't always better than copper alloy cores and always read up on the care of whatever blade you choose.

Also, lets talk about specialty blades such as CBN (Cubic Boron Nitride) . What CBM is, is a synthetic cutting material which has a cubic habit (just like diamond!). Does it cut metal better? Maybe, maybe not. When I used one for cutting some mesosiderite meteorites, it sure didn't last, and I had a full  tank of coolant.  The diamond blades that I use which cost 1/3 as much cut better and longer. . Why? I sure can't tell you. Maybe my rpms weren't "right", maybe the coolant I use isn't the best. But this blade which I spent $46 for won't cut butter now since all the CBN wore off. Are my diamond blades still cutting? Sure are and I'll stay with diamond. It's harder than CBN, it's crystal habit is the same as CBN, so there isn't a cutting advantage there for CBN. And it's cheaper and has a wider range of knerf thicknesses.