I'd take the
Roundabout out of the running. It has a shorter shell and only harnesses to 40 pounds. You'd likely be buying a new seat before you had planned on it with that seat.
I really like the
Marathon. It
RF to 35 pounds and then
FF to 65. As you'll soon find out...seats are more often outgrown by height before weight. It's an easy to use and install seat.
The Decathalon...I think you're paying extra money for infant pillows that you likely won't need...and many people have problems with the harness adjustor and the seat needs to go back to
Britax. It
RF to 33 pounds and then
FF to 65.
The MA and DC both have nice tall top slots and will likely get your child to 5 yrs in the seat before you need to buy a new one. You should also keep your child
RF to the limits of whichever seat you purchase.
RF is the safest way for all of us to travel---I wish I could!!
All of these seats can be tethered
RF, which will help with the recline. You don't want to be more reclined than 45 degrees, and baby can be more upright when they have good head control--and it's safer for them as well.
Post back with more questions if needed.
Susan