Question about powerleveling multiboxing

Hi all, i have been dual boxing for a whle now and just stepped it up to triple boxing yesterday. Anyhow i have a 70 shammie on one account and on the other 2 accounts i have a 35 priest, 40 warrior, 41 druid, 43 hunter and 43 lock, ohh and a 32 mage too. ANYHOW what im doing now is just running 2 chars at a time through ZF over and over using my 70 shammie. can anyone reccomend a better way to level them if there is one, secondly if i continue doing it this way at what level should i switch from ZF to another instance and which instance(s) thanks

Quests are really attractive. Naturaly not the 'collect 100 rare drops' ones. =]

Level 45 is the minimum level requirement for level 60 dungeons. I found nuking the mostly melee undead packs in Stratholme working rather well, using my tankadin to boost.
I am going to do some questing now, there are many lovely and stress free chains in the plaguelands.