Much more fun with friends.
If i can go with people that are somewhat enjoyable to be around i'd like that but if not i don't mind doin stuff solo.
I would raid with about 5 or under people that were my friends and in the same guild but not a big group of people.
I have yet to play WoW but in most multiplayer online games I prefer to work alone. Higher odds of me getting the spoils I want and not having to share them. :P