Corri-- Standard answer to the "best" carseat? "Whatever fits YOUR vehicle, YOUR child, and you will USE PROPERLY EVERY TIME."
That said, Britax seats are the easiest to use that I have encountered, and I've used about six or eight types at home and while traveling.

Personally, if buying a Britax, I would go for one of the higher weight limit seats. Since I don't have side airbags in my old, small car, I would buy the Boulevard model which has True Side Impact Protection (TSIP.) If you have a newer car with side airbags, or if your child seat will fit in the center seating position and you can manage to get the kid in and out from there (big ifs!), then TSIP won't matter to you.
Mere-- I PM'd you about that "extra" Roundabout...
We will borrow a bucket seat for the first 4-6 months. (That's how long DS fit his SnugRide.) My SIL is handing down a Graco SnugRide, plus another friend here has offered an infant seat, but I don't know the brand. I might take both and install one in each car, just to avoid buying an extra SnugRide base (SIL only had one.)
As of now, for DS, we have a SafeGuard "Go" seat in DH's car in the center positon (of an SUV.) This is a forward-facing only seat (FF) for an older child.
In my car (and another in my MIL's car) we a Britax Wizard seat (the pre-cursor to today's Boulevard--it had side wings.)
I plan to get a Sunshine Kids Radian for a second car (and travel) seat for the baby, and I plan to buy another Britax seat (unless Mere was serious about sharing...) for my car when the new baby outgrows the bucket next fall.
I've made this comment once before, but we did find that our son fit in a Britax Wizard Rear-facing (RF) from birth. He was full-term, 20.5" long, and wearing cloth diapers. (The seat's weight limit is 5 pounds, but a newborn is frequently too short to fit properly into the straps by height.) If you use cloth diapers, your kid will be about an inch taller in the carseat! If your family has tall babies, you might also be able to start off in a Britax.
I always recommend BORROWING (from a trusted friend/family member) the infant seat because so many kids outgrow them so fast,unless you know you are having more kids within the 5-7 year likely "useful life" of a new carseat...
--willo