As far as hunting whitetail deer either cartridge will work well.
I use a .45-70 partially for nostalgia, it's been around for over 130 years but the main reason I like it is because it can be hand loaded from mild to wild. You can hunt anything in North America with the round and some people have even used it in Africa on the "Big 5."
If you go for the .45-70 I recommend you pick up a copy of the book: Forty Years with the .45-70 Revised by Paul A. Matthews

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"Life is short, hunt hard"