I just bought one in .357, it's a ton of fun. I went .357 because of ammo costs and I already had dies for .357. I also like the option of shooting .38 Special out it. I know .45 Colt is the traditional caliber, but I want the flexibility of .357. You can't go wrong with either one.
.45 Colt's only problem is the brass is thinner than a .44Rem mag, so full house loads tend to lengthen the brass significantly, if you're doing a lot of them, it's a pain trimming and the case life is shorter