The only Animal Crossing game I've played is the one for the DS and I've only played the demo for Tomodachi Life, I think I'd have to lean more towards Tomodachi Life. Animal Crossing is okay to me but, for me, it's too broad. I didn't know where to start, I didn't really know where to go, it seemed as if it were a bit slow paced and I didn't have any friends to play with. Tomodachi Life is similar in a way with the gameplay most likely becoming a bit repetitive when alone but I've found that a lot of games that support multiplayer/online functions do tend to be boring when alone. Like I just started online competitive battling with Pokemon X and I haven't been able to put it down whereas before I may have played for literally five minutes, tops.
But, from my uninformed viewpoint (don't take my opinion seriously lol), I'd probably go with Tomodachi Life because everything is sorta laid out for you. You go to the overworld map, you have the little signs with the requirements to unlock the buildings and I can just jump in and make my own people and watch them interact with each other. I never really could get into the Animal Crossing series; I tried but it's too open for me--I'm the kind of person who needs some sort of stopping point or a goal or something so I can feel accomplished at the end of the day.
...And I just realized that's why I tend to play RPGs more often than not :/
But, yeah, I'm sure both games have their qualities and, maybe Animal Crossing: New Leaf is much better than the one I played but, if I were to choose, I'd choose Tomodachi Life for it's simplicity. Don't take my opinions to heart as I haven't even played either in their full splendor :/