Generally speaking, Shaman's (Enh or ELem) work best in larger cluster fights PvP (BGs, 5V5s, etc.) battles. When things get more "specific" like 1v1 or 2v2 Shaman's suffer and don't do well.
If you pull up the armory and look up Shaman's in Arena teams...You generally don't find a Shaman of any spec, anywhere in the top 10 (especially in 2v2). 3v3 and 5v5 you'll start to see team combo's that have Elem and Resto specs, but not Enh.
Enh specs are a kiting to death, waiting to happen. Given the fact that most (if not all classes) have some form of reliable CC (and Shaman's have NO form of Anti-CC), this makes things difficult. While Enh burst dmg can be some of the highest in the game, its still based on a 13% gamble. The gamble being that we're reliant on WF procs. Since we lack Anti-CC, lining up all our ducks, so to speak...comes rare. Thus, your relying on someones "mistake", rather than a reliable strategy. Due to the nature of focused, Arena players..."mistakes" are few and far between, so you can see where the problem lies.
Elem tends to have some specific advantages, specially when the team size gets larger. Elem's burst dmg can be scary! Honestly, well geared Elem shaman can put up a very believable arguement to "who does more burst dmg" when comparing shaman specs. The most dmg I've ever done in a single hit as a Shaman was as a Elem (3k+). Factor in the remote possibility (5%) that the cast can be duplicated, and shock following that up...thats alot of dmg! Not to mention that WF procs can't scale up...thus your always stuck at "praying" for the 13% to happen. But, bolt crits CAN scale obviously due to gear, and a hypothetical 30+% and "X" amount of spell dmg can account for more reliable "burst" amounts. Not to mention elem gear helps more with occational PvP healing than straight up enh gear, and thats not a bad thing. Not to mention, having range dmg always helps get in a few hits on someone before then get to melee range. Course, the problem is as you might have noticed, once you got someone in your face, its very difficult to get them outta your face. And when taking a beating, 1.5 seconds becomes very LONG to get a single shot off (assuming you have it talented).
I've played each spec of Shaman for long periods of time, and found the most success in arena (and PvP in general) as a Resto (btw...I HATE the spec, but I give credit to where its due). But, after experiance...I'm partial to suggesting that Resto IS the best PvP shaman class.
This being said...I'm a Enh/Resto now myself, and do the occational Arena with my GF's Dest Lock, or 3v3 with a guildys (generally a mage and another Enh shaman). I can safely say, that these are BAD combinations for arena teams lol! If I had more "choice" of class combination or more time to focus on arena, I believe a "better" class combo with a Shaman (namely Elem or Resto) would be something like a Druid or Warrior. Further more, as I already suggested, find larger arena setups...3v3 or 5v5 for best results. Stray away from 1v1 conflicts as much as possible, generally speaking. This does not mean that your shoe horned into JUST healing, but rather the fact that standing in the background for even a second uncontested, can spell defeat to thoughs who don't respect the range dmg potential of a caster shaman.