I'm pretty picky. I have a set 5 villagers that I've kept for basically my entire play through, and then rotate the rest of the plots. I mostly tried to experience many villagers in my favorite species, while earning their framed photos. During this time I've tried to gain some other villagers that I haven't really ever had in any other AC games before as well. I definitely don't go for random villagers though. Instead I try to hunt for ones that I haven't gotten their photo (and I want it), or villagers to trade.