I want to level the following classes to 80 as easy as possible:
Given this stated intent, it actually makes no sense whatsoever to level two of the same class, even just while you find your feet with boxing.

If you don't have any specific prioritisation (i.e. you don't care what you get first) then go with mage + warlock for your first pair. The pet will tank, and the DPS will.... well, DPS.

And they synergise well enough to get away with just a /follow and /assist macro for levelling.