My first pick would be another ele shaman. It would be the easiest to do in a raid. You become a 2 for one deal and you wont have to do any kind of setup for situations where things work for one toon over another.

Other thing to look at is loot. Do you get counted as one person or two. Might suck competing with yourself to gear two like toons vs going with a leather or cloth user if you get to count each raid toon separate.