honestly i personally have seen both classes own in pvp.  in pve it is deffinatley prefered to be elemental, cause rogues and dps warriors fill the need pretty well and u have less a chance of hurting the tank in some fights (ie: Gruul).

About the elemental shamans in 5v5, there was a team of 5 elemental shamans on a European server that had a 2200 rating at one point in time.

Whaterver spec u choose it is all personal preferance, honestly i would go elemental.  plus your flame tounge damage is increased as your bonus spell damage goes up.

Elemental shamans are heavily dependent on crit in endgame, and enhancment are highly gear dependent to be even somewhat efficient.

But this is coming from a guy w/ a 70 resto shaman and a 20 elemental shaman