T.J.
The most important thing is the safety rating! We have always gone with Britax because there is no doubt that they have the highest consistent ratings. And they're very cushioned, comfortable, and durable. The Marathon model has a removable cover that you can wash, which has been great! In addition, we were in a really bad accident once with this carseat and my daughter was fine. I immediately bought another one, which her little sister now uses and we got her the Britax Frontier, which is their high back 5-point harness booster, so she can stay safe even longer! The other thing to look for is high weight and height limits. The britax roundabout can only be used up to 40 lbs so you will have to buy another seat earlier, the marathon goes up to 60 or 65 lbs! My tall four year old still fits in it and still has 20 lbs to grow out of it! The only reason we moved her to their booster is so her sister could use the marathon.