Drew mentions that he doesn't see the Mountain Guns shooting quite as well as the standard guns. I agree with him. I also agree with the thoughts above. S&W put the heavy barrel on Model 29s for a reason. It makes them much easier to shoot accurately, IMO. I think MGs inherently shoot very well, but, as a practical matter, I believe they are just much harder to shoot with the same precision as guns with the target-contour barrel. Something to consider.

With that in mind, if you want the tapered-barrel gun, the .45 Colt might be a better choice, particularly if you do not handload. Shooting full-steam 44 Magnums in a MG is not an enjoyable thing. If you handload, it probably could go the other way. In that case, you can make either caliber do whatever you need, and if you take your gun away from home, hunting or whatever, you can find 44 Magnum ammo almost anywhere - if you lose your supply. The Colt is a bit harder to find. If that is a concern, the decision might tip slightly to the 44 side.

My own MG is a square-butt 629, but if I could have rigged up a similar 625, I might have. Either gun will be nice to have, but you will end up shooting more .45 Colt-level loads no matter which one you buy, so the .45 may be the most logical choice.