The car seat world is massively confusing, can be quite expensive, and is totally mandatory for you to weed through if you are or are becoming a parent! There are many brands, and even stages of car seats, and differing advice floating around out there.

I hope to alleviate some of (most of?) the confusion.

First off, some guidelines that apply to car seat safety and children:

1)In theory no one seat is safer than any other. All seats in the USA must meet the same safety standards. However, some seats exceed those standards. Features that make a seat easier to use make it less likely to be used incorrectly, which makes it safer. And features that enable the seat to be used longer with a child enable a child to stay in a seat which makes it safer. The American Academy of Pediatrics says the safest seat is one that fits your car, fits your child, and will be used correctly 100% of the time.  Note that not every seat will fit in every car.

2)NEVER purchase a used car seat. Its actually unsafe to get a used car seat unless it is coming from a trusted friend or relative and you are 100% positive:
1)it has never been in any wreck
2)it has all the original pieces, including manual
3)it has never been dropped, which means never been checked as luggage at the airport, either, since this frequently happens when checked or gate checked .
4)it is less than 6 years old
5)the straps have never been completely submerged or washed with anything other than mild soap(it messes up the flame retardent treatment)
 
If you wouldn't trust the seller with your child's life, don't buy a car seat from them. For $40 you can get a Cosco Scenera from Walmart. It rear faces to a whopping 35lbs, which is important b/c kids should stay rear facing as long as possible, the American Academy of Pediatrics says keep them rear facing preferably for their first 2 years of life. Then it goes to 40lbs front facing. It won't last child as long forward facing as some others, but for $40, its a great deal. Or, call your local police station and ask about car seats. Most have programs in place to give free/inexpensive car seat to families that need them.

Stage1: rear facing. Kids should remain rear facing as long as possible, preferably until at least 2 years of age. Turning kids forward facing at 20lbs/1year is an outdated practice that could cost you your child. A forward-facing child under 2 years old is 4 times more likely to be killed or seriously injured in a crash than a rear-facing child of the same age. A child's vertabrae do not fully fuse until 3-6 years old, before then, she is at great risk for internal decapitation. The spinal column can stretch up to 2 inches in a crash BUT the spinal cord can only stretch up to 1/4 inch before it snaps and baby is gone. the American Academy of Pediatrics recommends keeping baby rear facing until he reaches the maximum of his rear facing convertible car seat, all current ones go to at least 30lbs.

Stage2:forward facing. Once turned forward, kids should stay forward facing in a 5 point harness as long as possible, it offers infinitely more protection than just a seatbelt and booster (which is a 3 point harness).  Most convertibles go to 40lbs, but Britax Marathon/Decathalon/Boulevard goes to 65lbs, Evenflo Triumph Advance to 50lbs, Fisher Price Safe Voyage Deluxe to 55lbs, there's many that go past 40lbs. Keep 'em harnessed! To correctly sit in a booster, a child needs to be able to have the lapbelt go across their legs (lap) NOT their belly. And the shoulder belt go across their shoulder, NOT their neck. Their head also needs to have reached the stage where it is more proportionate to the rest of their body, more like an adult’s. Kids under age 5 have higher rates of head injury if they are riding in boosters than kids over age 5 because they have heavier/larger heads in proportion to their bodies, so they fly forward farther or with greater force.  Remember one of the reasons babies, toddlers, and preschoolers are so cute? Their head is so much bigger than the rest of them! Wait till that effect goes away. Also, a child’s spine is not fully solid like an adult’s is until age 6.

Stage3: booster seat with seatbelt. The bare minimum for safe booster use is 40lbs AND 4 years old. But many 4 year olds aren't ready to sit properly in a booster. 5 years old is a better idea. Only use highback boosters, not the no back ones. No back boosters offer no protection whatsoever, they only boost the child up. Use a booster until the child is at least 4'9" tall and 80lbs, the minimum to safely sit in a seatbelt alone. Most kids need boosters until age 8-10 years old.

When buying a seat, look for deep side wings to provide side impact protection. For newborns, look for seats with low bottom harness slots (8 inches or less unless you expect a big baby). For older babies/toddlers/preschoolers, look for tall harness slots (most seats come in at only 14-15”, though some have 17” or taller) and high weight limits. These are things that will help insure that you get to use your seat for a long time.

Remember: the BEST seat is the one that fits your child, fits your car, and will be used correctly 100% of the time. (This is why convenience features DO make a difference and ARE worth the money! If its easy to use, you're more likely to use it correctly. Another important thing to consider is how many you need. Many people figure they will just move a seat back and forth between several vehicles. Not a good plan. This exponentially increases the chance that the seat will be installed incorrectly. If you are a 2 car family, plan to purchase 2 seats. If your child rides in other cars (like grandparents) frequently, purchase them a seat to keep installed permanently, or purchase a spare to keep at your house for using in when your child goes with them, or you perchance have an extra little one with you.

Try out different seats!! Make sure you are comfortable with the one you choose – it does NOT have to be an expensive brand to be a good seat, but keep in mind that as with everything, cheap often means just that. Don’t plan on getting by with a $50 car seat and then later a $20 booster. It will not be enough to protect your child for the amount of time he/she will need to be in a seat.

--Seats to steer clear of, no matter what stage your child is in or coming near to.

Shield boosters. These aren’t even made anymore, and for good reason. Children are at nearly eight times higher risk of serious injury when riding in these seats.

Shield Boosters provide little or no upper-body protection. In many cases, the children who are injured or killed in these either:

Get flung too far forward, resulting in serious head or spinal injuries or

Submarine UNDER the shield and have spinal/neck injuries or are actually decapitated.

There are also unfortunate cases where children are thrown OUT in a side-impact or rollover collision.
****"Kathleen Weber (University Of Michigan Transportation Research Institute): Shield boosters are no longer considered appropriate crash protection for children. Crash investigations have documented ejections, excessive excursions, and shield-contact injuries in rollover, side, and frontal crashes, resulting in severe head, spinal, abdominal, and extremity injuries."

****"Web MD:  There's more evidence against shield-style child booster seats. Children are at nearly eight times higher risk of serious injury when riding in these seats, a new study shows.

  Another type of seat to stay away from – overhead shield seats. (OHS). These are the ones that have the bar that comes down over the child’s head to rest somewhere between his/her lap and chest. Safety experts have concerns about CRs with shields. Tray shields are not usually covered with energy-absorbing padding to protect the head if it hits the shield. This contact is more likely with a shorter child and a loose harness. In a test series with a 12-month-size dummy, peak head acceleration was 35% higher for tray shield restraints than for 5-point harnesses. At least one child (19 lb) is known to have received a fatal head injury from contact with a tray shield. For T-shields, there is a concern that the throat of a small child may be injured from contact with the top of the shield during a crash. In the same series of crash tests, neck forces were 40% higher for T-shields than for 5-point harnesses, and the crotch load with T-shields was 2.7 times higher than with 5-points. See Weber 2000.