Do you reload? If so, definitely the Ruger hands down no question. The Ruger SBH/SRH will handle the abuse of some really hot handloads. If you don't reload, I'd get the .44 mag because factory ammo in .45 Colt is expensive and there's not as much variety as there is in .44 mag. Well, the .44 mag isn't cheap either, that's for sure. Even the .44 specials are expensive.
If you reload, there's a lot more debate between the 2 cartridges. They are both extremely versatile cartridges for the handloader. If you don't reload, you should definitely start....especially when you're considering those kinds of cartridges.
There's lots of used SBH .44s out there for cheap. I'd get one of those if they feel good in the hand.