We used a Cosco Scenera for two years. It's a great seat--lightweight and easy to install. Unfortunately my kid got too tall for it just before his third birthday.

We are now using an Evenflo Maestro. It's not terribly different (there are a couple of minor differences in the install), but can be used as a 5 point harness for kids up to 50" tall and then as a high backed booster after that. My kid is now 4 and >40lbs, so we switch off between that and the bubble bum inflatable booster for car rides.