Jeff,
The hydro is pretty much the same on a 149 and a 1450. Early 1450's had external disc brakes, later 1450's had internal brakes in the transmission. Other differences on the 1450 are: Magneto ignition and a flywheel starter instead of a starter-generator on the 149, electric PTO instead of mechanical, side panels on the engine compartment, rubber ISO mounts for the engine, rag joints at both ends of the driveshaft, hydro speed lever is different. I may be missing a few details. I believe any attachments that work on a 149 will work on a 1450 and vise-versa.
As far as which is better, well that a personal opinion. I used to think the 149 was superior, due to it's simpler design, but I've come to think that most, if not all, the differences on the 1450's are improvements. Of course, that's just my opinion, and it's worth the price you paid for it!