Well depends if you like First Person Shooters more than "Character Action" titles.
I haven't played Far Cry 3 so I can't speak for it's quality or how engaging it is in the long run but I had a ton of fun with DmC. It has a solid campaign with some good length to it - I think around 10 hours first time through. The gameplay is a lot of fun and the pacing is great, introducing new areas and new weapons up until the very end of the game.
Far Cry is pretty good. Its a longer game if you're only going to play once, but I would guess DmC is more repayable. I think its down to buyers taste.
Also this is a weird bug:
EDIT: Huh, I didn't even know you could make multiple choice polls.
Far Cry is a really good game. If you want to roam around, punch tigers in the d*ck and burn fields of cannabis, then Far Cry 3 is your game my good man.
DmC seems like a really well-made, interesting game. I never played any of them, kinda wish I had, seems like the series offers some genuinely good plays.
Far Cry 3 is a lot of fun, so that's my recommendation. Keep in mind console versions have some pretty low frame rates, but look stunningly good all things considered (it's not unplayable and you get used to it after an hour or so). As usual, the PC version the the version to get but I find navigating the UI via mouse and keyboard to be a pain.