Well it kinda depends on what you want...I've shot all three

.50 AE: Very powerful, expensive ammo, lots of recoil but manageable

.44 mag: Very powerful (will kill anything the .50 AE will), large selection of cheaper ammo, a medium amopunt of recoil which is not bad at all to shoot.

.357 mag: not as powerful but powerful enough for almost anything, big selection of cheap ammo, hardly any recoil at all, will shoot very fast and accurate because of low recoil.

It all depends on what you want.