The Draenei racial is nice with the added hit bonus along with the Gift of the Naaru HoT(stackable), but it's really not a huge deal when it comes to Elemental Shamans, considering the amount of hit you get from talents and ToW already. And if you're focusing on primarily doing dungeons then it doesn't change much having it or not.

Having the Troll racial might be nice if you save it for the more difficult dungeon bosses earlier on (until you're more geared, then using it or not really doesn't matter too much) - Though stacking Berserking, Drums and Lust sounds pretty awesome. Personally i'm going Orc for their look, and because i plan on doing atleast some arenas and wpvp along with plenty of dungeons, so their racials cover everything that i'll be doing.

All things considered, in the long run any of the races are going to be more than viable for 5x Shamans, just pick what works for you.