Really depends on how the group mechanic will work. Having lots of small team's will help open door's (maybe), but not really be effective against a well defended area. Having a large group format, based on army ranks for example, tends to have less talking and move co-orderdinated approach to situations. Rank is based on the ability to learn and lead, rather than rank for sake of rank which works in other mmo type games.
Whilst I personally like small groups that can run off and do their own thing without worrying about the larger picture, great for those down times of few people, I've been in enough HUGE/cap locked battles, with large team structure, that small groups are really for greenie, solo players who will die a lot.
It's your choice, how you play, but personally..... I'll enjoy my time either way.