Cybex, Britax, Diono, Maxi Cosi, Nuna, Clek, Chicco, and Uppababy are the leading brands in carseat safety. Many people turn children forward facing as soon as they turn two. This is very bad. Just because you can doesn't mean you should. Little kids necks are very fragile and it is up to five time safer to face the rear than forward facing.
Another problem is that people take there kids out of carseats in favor of boosters. A full harness keeps children in the ideal position even when asleep. There is a reason that racing cars are equipped with five point harnesses. Because it's safer!
Clek seats are designed by the best car companies in the world. They take the technology that makes cars safe, shrink it, and put it in the carseats.
The new Cybex Cloud Q infant seat has a full recline when you take it out of the car so your baby can sleep at a pediatrician recommend angle. It also features Linear Side Impact Protection.
Britax is, well, put it simply, one of the best brands on the market. It's patented honeycomb-shaped impact absorber is revolutionary.
Just because your child is tall, or heavy, or in 4th grade, doesn't mean you can't find the right seat for your child. Diono makes good ones for older kids.
All in all, I think safety is number one for all parents, but most people don't realize that you can, and should, keep your kids in carseats for as long as possible.