Depends on your play style and what you want as a main toon in the end.

Originally I picked priest and warrior so I could have them quest together. Eventually I spec'ed them holy/prot and was in a guild that whenever they needed one or the other (often they wanted both) for 5mans or raids we were golden.

A lot of people have support classes and a dps/grinding alt, so a (healer/tank) and a (rogue|hunter|warlock).

So if you leveled a hunter and a drood. You could spec ToL on the drood eventually and have a nice hunter to grind motes/leather with, do some dps fun stuff and never feel the downside of the ToL.

I think you will enjoy it so much that you wont want to merge the accounts. There is just no saying no to a well grouped pair of toons.