To be honest, its not going to matter too much. The only real issue with 12 spawn maps, is that when a round first starts, you'll have some players inside of other players. Most of the time, thats not the sort of thing the majority of players are even going to notice or care about. I would go with 16 myself, because it just looks nicer, but its not really a huge deal, unlike counterstrike where a map with 12 spawns could end up having players spawn inside of each other in a 32 player server.