We LOVE our Britax Roundabout! It was definitely pricey ($200), but super safe (though your past this stage, I think its the only car seat with the rear facing tether), and SUPER comfortable, which was really my main reason for splurging on it (that, and that it matched my car interior! LOL!). After reading the Consumer Reports reviews of car seats last year (I think you can access that through their web site), it seemed like MOST of the car seats had very comparable safety records. So it really came down to comfort, style and ease of use for us. Since I figured DS would spend quite a bit of time in the seat, I wanted it to be comfy...cozy....and easy for me to manipulate. The Britax has been that for us.
With the next babe, my plan is to use the Britax right from the beginning, instead of messing with the infant/ carrier thing. I figure DS will be in a booster by then, so the timing will be perfect.