I was recently researching carseats, as I needed new ones for an infant & a three year old. www.car-seat.org was an invaluable source! After days & days of reading the forum there and checking out different seats, we decided to go with the SafeGuard Child Seat (not the Safeguard Go booster) for our three year old. So far so good, but head slump has been an issue when she's sleeping. We couldn't find anyone local who had one to try, but as much reading as I'd done, I was sold on its safety features; the site from which I ordered it (elitecarseats.com) has a five dollar return policy, though, so we opted for that incase we needed it.
We chose the Britax Boulevard for the baby. We looked at the Recaro, as someone else suggested. It really is an awesome seat & I would have chosen it for the baby, but read from other owners that it's a bit tight for chunky kids & my baby is proving to be a bit of a nugget.
I didn't worry about getting one that converts to a booster for the 3 year old, as I figure by the time she's big enough for a booster, there will have been more safety innovations.
Please do check out the link. You'll find reviews, knowledgeable carseat techs, safety suggestions, pictures, info about what seats work in wehich cars, all kinds of info to help you make the right decision!
I think Albeebaby.com is having a pretty good sale on their older Britax models at the moment.