For me its all in the name. I will not join a FC that tries to "be cute" with their FC name (or one that just completely lacks creativity and imagination). Often when I join a FC or <insert name of guild-like system in whatever MMO> I end up trying to find a balance between enjoyable people and a FC with a name that I can "live with".
There are other things as well, such as it taking more than a good party or two with some people from a certain FC before I can get a good idea of their personalities and if they would be people that I want to associate with.
