Fastest way to level two chars on different accounts together?

I have two accounts on which I want to start on a new server, which class combinations would get me to level 90 the fastest and what method should I use to level them? Instancing, questing, etc?

 

Questing have always been the fastest way of leveling in wow.

You could etc do Multiboxing now since you got two accounts (why not) and use two of the same class or use a tank/healer or two dps and hope for you can nuke mobs before they get ya.

 

What kind of multiboxing software would you recommend? I've never tried such a thing but it sounds interesting.