Oh, where do I start?? LOL!
After an infant carrier car seat the next step is a rear facing convertible car seat. Definitely keep your baby rear facing until
at least 12 mos.
and 20 lbs..
Longer is even better! The AAP and safety experts now recommend babies stay rear facing until they outgrow the rear facing limits of their convertible car seat. Rear facing better protects the head, neck and spine during a crash.
More info and video clips:
Car Seat Safety for Your Infant | Partners for Child Passenger Safety - Children's Hospital of Philadelphia CPSafety - Your online child passenger safety resource
I love Britax seats, but they aren't within everyone's budget. Whatever you get, be sure it has a 5 pt. harness (not a shield!) and a front harness adjuster.
CPSafety - Your online child passenger safety resource
I would like to mention a car seat worth checking out, if you can find one - the Fisher Price Safe Voyage Deluxe. It's made by Britax for Fisher Price, and is essentially a Britax Marathon without all the bells and whistles for about $130. I have one and LOVE it! Unfortunately, this seat has been discontinued.

WHY, I don't know.
Fisher Price Safe Voyage Deluxe Convertible Car Seat in Black
The center rear position is typically the safest because it's furthest from all points of impact, however, if you're unable to tightly and correctly install your car seat in that spot, it's not a safe option.
To find a Child Passenger Safety Technician in your area:
Home | SeatCheck.org
More Car Seat Resources:
Resources - Child Passenger Safety - ParentingForums.org
HTH
