If you played a bit already - or follow some guides (like the RAF tourguide) you won't have a problem getting a pair to 60 in a few days /played - so I would think: focus on what you'd enjoy playing more than how fast you can get there - because what good would the toon be to you if you don't like the class once you reach 60 ?

Beside that, I recommend having at least 1 class who can heal/rez out of the 2 - and 2x the same class is easier to setup - in RAF time you can probably, even without burning out (you can burn out if you over do it) get at least 2 pairs so you could do more than 2 classes or 2 classes in 2 pairs (e.g. 2 druids and 2 pallies)