I am a father of 3 kids, including twins. I've had all brands of car seats, and it really varies from models to models. What i like best is when you can ajust the height of the straps without taking the seat out of the car. If you have, or plan to have more then one kid, the footprint of the seat is also important. Trying to fit 3 seats in a impreza, you need to chose them as narrow as possible. Sunshine kids makes great seats that you can carry around easily.
We totalled our 2007 Nissan Quest in an accident. One of my kid was in a eddie bauer, another one in a sunshine radian, and the last one in a graco, the 3 kids were safe and sound.