Ammunition costs, even reloading, 38/357 is way more economical!!! Recoil is much less from a down loaded 38 with a 110 grain bullet than a mid range load from a 45 with a 250 grainer! This makes aligning with the next target MUCH quicker, so if you have a limited budget, or aspirations of becoming one of the speed demons (and I say that with respect, some of these folks are so smooth in their shooting and transition to another gun they only LOOK slow), 38/357 is the way to go.
Don't for get the vaqueritos in 32! There is also the old traditional cartridges, 32-20, 38-40, 44-40, and then too the 44 special, colt, russian, magnum, 45 scofield.
I guess the best sass, 'scuse me, cas cartridge would be the one you already have, or the one you like best.
Butler Ford