Fantasy life is overall better game but
But If you have A LOT of friends in your 3ds that regularly play acnl then acnl. Acnl is not something you want to play alone. It does not have full online multiplayer, it has something where you can only visit a friend's town if they are your 3ds friend. I got 40-50 acnl friends that regularly play so it's more fun for me. Also, if you get acnl then you're going to need some free time. After a few weeks you will be forced to play 30mins to an hour a day if you don't want to mess up your town. So if you can only play 3ds every few days or only on the weekends then don't get it. Fantasy life how ever can be played like once a week without messing up anything in game
I don't have fantasy life but I think it's a better game overall single player, it has online multiplayer too so that's good but if you have a lot of friends that play acnl or are going to try and add a lot of friends from 3ds pedia that play it to acnl then get acnl.