Either caliber would be fine. I personally own the .450 and use it almost exclusively for deer. I've been using the factory Hornady 350 grain loads and they work great on whitetails. I've shot 8 so far with it at ranges of 120 yards down to 7 feet. I personally like new stuff, not nostalgic stuff like the .45-70, but the honest truth is there is really little practical difference between the two. If you can't handle recoil though, you shouldn't buy either one.

I think I'll continue shooting my .450 and let those .45-70 guys enjoy their antiques.