Level 1-8: questing - often single and not multi
Level 8-14: Ragefire Chasm
Level 14-20: Wailing Caverns
Level 20-40: Scarlet Monastery
Level 40-55: BRD then LBRS
Level 55-65: Ramparts then Blood Furnace

I can do this using a 70 warrior. Although I have 4 warlocks, I'll often pick up a healer and just rotate 3 warlocks. The healer speeds things up, he can also loot things. My general rules are he can keep everything that isn't rare, which I get to keep. If it's rare and something the healer can use, then it's his. The xp is so fast there are few complaints about the loot rules. Some people just don't get it and want to loot every little grey item and spend 15 minutes running back and forth selling when we could just pick up the expensive stuff and make more money/xp faster.

BRD and LBRS in particular are underused I think. The mobs come in nice groups of 4-5, perfect for a warrior. One of the nice things about both of these is that they are so large I'm able to just bang away for 45 minutes, clearing it and avoiding the shuffle at the zone line that is always so annoying.