With three toons to grant levels to, why not try a paladin, druid and some other DPS class -hunter, lock or mage? Then once you're done, start a DK and see how that feels. I currently use a paladin for a tank and I enjoy it. I was never a melee type but I actually enjoy playing a paladin. You might run into some limitations with a druid tank at some point, but others would know more about that - maybe due to gear availability??

Also, you can level your shaman to 60 and grant to 60.99....I am pretty sure, heck I already forget =) There are other threads on this you can search for to confirm, but I am pretty sure this is what I did with my second batch of toons (didn't think you could when I did my first batch).