Convertible Car Seat

With Black Friday coming up, I see that Wal-Mart will be having a sale on the Diono Radian 3RXT. The other car seat I’ve been eyeing is the Britax Marathon. I’ve seen complaints that the Diono doesn’t fit rear-facing too well and you either have to bring the passenger seat all the way to front or buy a wedge for about $25 to angle the car seat. Which convertible car seat would you recommend?

(My son is almost 17-months old (a bit on the short side) and he still fits in the UppaBaby Mesa bucket seat. With the winter gear on, he’s getting quite snug in there. Height-wise, he may have 2 months left in that infant seat.)