B.W.
The Radian seats are GREAT seats! My best advice is to go where you can try it out both rear and forward facing in your car. The Radians have low belt paths, and some cars are completely incompatible with the seat while using the seat belt because thier belt stalks are stiff and will not go throug hthe belt path even with the approved 3 twists to the stalk. You can use the LATCH only up to 40/48lbs, then you must use the seatbelt after that weight.
Also, I would not get the 80 unless your child is short and heavy. THe Radian65 and the Radian80 are the same height, they are just approved for different weights. So if your child is of average or smaller weight, then the 65 would be just fine. Case in point, my 5 1/2yr old is 49'' tall, and 48lbs, and still has room to grow in the Radian65. The extra money for the 80 would be well spent if you had a short heavy child, but if your child is of average weight, then hte 65 would suffice.
We own a Britax Marathon for our youngest, he rear faced in it until 21 months and 33lbs, 36'' tall. He's 2 1/2 now, 37'' tall and 35lbs and still has at least 3yrs left in the seat. My oldest rides in the Britax Regent, which will harness to 80lbs but is a big, heavy, forward facing only seat. You need a seat that will rear face (keep her rear facing as long as possible!).
The Marathon is slightly wider than the Radian seats, but not by much so fitting three across in the back seat would be no problem with the Marathon either.
I would toss it up between the Marathon and the Radian65... the are comparable size and safety wise... but the Radian CAN be incompatible with alot of vehicles, so USABaby has both in stock so you can try them out in your car. I prefer the Britax Marathon simply because I've installed it in at least 7 vehicles and its had a great fit every time.
