World of Warcraft PvP Guides - Party and Raid Buffs Guides
Since each group is different, how you balance in the best buffs for your group is really up to you. Some groups will focus on getting the most DPS so that they can speed through the instance or raid, while others will focus on buffs that ensure the healer and tank are maximized. It comes down to personal preference, the buffs available, and which classes are best geared to go without buffs.
As shown from the list of best buffs above, the buffs that stack up best in a group makes finding a few key classes / specs critical for your groups or raids. If you are doing simple content that you over gear you probably can take any classes that you want, but if you are doing difficult content for the group it will be worth your while to pay attention to the buffs available while building your group.
The best classes to provide buffs really depend on your group though, so there is no overall best for all situations. If you are a melee heavy group you should be looking to include a paladin, warrior, shaman, death knight and druid.These five classes interact extremely well and provide buffs back and forth.