First, I read the previous posts . . . and you ABSOLUTELY need at 5 point harness for safety.
We have several carseats and here's my opinion.
Britax: We have the Roundabout and really like it. It *looks* more comfortable than some of the other seats and s super easy to install. But, it is very heavy and difficult to travel with. I initially bulked at the price, but your child is going to be in it everyday for at least a year, so cost per day really isn't that bad. However, if I went the Britax route again, I would by the Marathon since my older child (who is small framed) outgrew it sooner than I thought he would.
Evenflo: We bought the Titan as our 2nd car/travel seat. I am not sure if they make this model any longer, but has been a great seat for air travel. Super lightweight and easily adjustable. It got top Consumer Reports ratings in 2005 when we bought it.
Cosco: When my older child outgrew the Britax, we recently bought a Cosco brand seat from Target (not Costco, the store) for about $45. I also really like this seat. It does not sit as high off the seat as the other two (because it is a booster as opposed to a front/back convertible) so I don't whack my son's head on the door of the car EVERY time I put him in. LOL It can take a child as small as 22 pounds which my younger one was at 1 year. (He's still in the Britax, but we have used this one in a pinch.)
One other thing to consider is how the seat will fit in your car. For example, a Jeep Grand Cherokee has puffy seats, so it is really, really hard to get a sit fitted properly. Likewise, the seat length on a Mazda 3 is really short and the Britax hangs over. If possible, go to a place like Babies R Us that will let you fit the display in before you buy! There are simply too many choices!! Good luck.