We have a Britax round about. You can use them forward or rear facing an its safety rated from 10 to 90 lbs. (Although, I cant imagine a 90 pounder still in a carseat). I have always loved this carseat. It's really easy to tighten and loosen, the straps never get tangled and it seems to be a very comfortable ride.
We also have the Britax booster (for older children) and I'm much less impressed with it. I wish I bought a second round about. The booster doesn't look all that comfortable and I don't like the mechanics of how it attatches to the car.