M.S.
We have 2 Britax Marathons and LOVE them. For a slimmer profile and to have your child not kicking the front seat as much, you can also go with the Sunshine Kids Radian65 or Radian80. We have a Radian80 - we LOVE it and it's less expensive than the Britax...good up to 80 pounds in a 5-point harness, folds so you can travel with it easily, is comfortable (she was great for a 4.5 hour road trip), and is a little less expensive than the Britax. If you want function for a lower price, we also have 2 Cosco Scenera seats (in Kentucky at my mom's), which are highly rated for safety, but not great for long road trips, and cost $45 or so. The Britax is by far the easiest carseat to install.