Warrior + Shaman

[nodoze]

If you plan to PVP the main thing I would recommend is that you decide which character will be your "main" (pun intended)...

By "main" I mean the character that you would chose to play when you go into places where multiboxing doesn't work (like in BattleGrounds like Warsong Gulch, AB, AV, etc) or where you go into places where multiboxing isn't typically welcome (like Progression Raids in a progression raiding guild)...

Once you decide which is your "main" I would try to mainly (pun intended) drive from that character.

The reason I recommend that is because it should make it more natural and you should perform better when in PVP or challenging progression PVE...

That isn't required by any means and for example you may find it too awkward if you plan to main a healer and are driving your team from the healer. That being said it may be that you find it a natural fit for you and help you be better when you are not boxing.

Bottom line is that in a PVP game that is something I would at least consider up front and try.