I havent tried DK tanking but it seems alot of people have some great fun with it.
Ill let someone else field that one ;]

One thing i would throw in ~ if you going to level groups you might think about leveling a mixed group.
There is a bigger learning curve to running a mixed class than it seems at first.

Leveling a mixed group to 60 you will be able to roll right out of the gate with your ideal group.
Otherwise i would expect a lot of wipes before you got comfortable with the different play style.

All of your groups sound appealing ~ hunter mage might be faster gearing up with no drop competition.