I would really say it depends on what you are trying to do. Mage pets can tank fine for almost all situations (except for the mobs that pull you in....), shaman is great for many things, bst can replace a shaman in many instances and if this is a main char could help tank/offtank, and pet at higher levels can tank decently, druid can be nice with the mag bst since it can add extra healing/pulling with fade, snaring, etc, or can use a real tank class and have the mag pet be more dps. SK have a lot of advantages for tanking with a mage as they can do some slows and such, paladins can heals quite well, warriors can take the punishment. Necro can also slow and are amazing when used well. So overall if you 3 box...the combinations are almost endless what you can do depending on how you want to balance your group. Almost any class can be paired with the right group using mercs and 2 other bots, you just need to choose how and what you want to be doing with them.