I exclusively 2-box (mainly because my system won't handle more than that). If you want to run a same-class team, you can't go wrong with 2 hunters or two warlocks. The pets increase your survivability greatly. They both have good cc. The locks allow for healing through affliction talents.

Other good combinations are tank/healer combos: pally/pally, warrior/priest, feral druid/resto druid, etc. The trick here is to set up your key bindings so your tanks skills are separate from your healing skills. I use the number pad for healing and the regular number keys for tanking. It will take a little getting used to but, it's really not that bad.