I went with the 460 like the other guys said, as far as versatility it can't be beat. I found the lighter grain hornady loads pretty cheap considering. I also reload so instant brass.
I opted for the .454 Ruger Super Redhawk.
I reload the .45 colt rounds with the same 230 grain bullets that I load for the .45acp.
I use the same powder too, so it seems pretty economical - if you reload.
Last time I saw a box of .45 colt they were pretty expensive and they were light cowboy rounds.
It'll cost you about a buck apiece for .454 ammo.
I don't know what .44 magnum costs.
Out of identical guns they both feel like cannons.
The .454 is just a bigger cannon.
I like the idea of the .460 though if you're thinking of buying now.
It just depends on how often you plan to shoot it.
.45 colt is cheap, everything else seems to be pretty expensive.