It becomes necessary to learn the biggest benefits of each class after each individual patch, the specs of each tree, and the general leveling specs can definitely change. Sometimes \

If you have been playing a Shaman in WoW, you know how incredibly versatile your character is. That flexibility translates into impressive abilities. Think of it: ripping up the enemy with Windfury while your totems make torment your enemies and keep you safe from harm.

If you're skilled with this class, Shaman PvP combat is incredibly fun. But because a Shaman can do so many things, there's a significant learning curve you need to navigate before becoming good at player versus player combat.
Level 1-30
Some people will tell you to go enhancement on these stages, because you'll have much less downtime. While this may be true, even if you have no downtime at all, you're going to take forever to kill monsters because you're not doing nearly as much damage with enhancement as elemental, especially before you get dual weild in the enhancement tree at levels 40+. You can go elemental, equip a shield, and find all of the spellpower gear that you can find, even if you have to use cloth, because your shield will make up for the loss of armor.

Level 30-50
This is a tricky level range, but it’s better to stay with elemental from levels 30-40, because you still won't have dual weild before this, and enhancement will still be quite a poor leveling spec. In fact, if you really want to go enhancement, It’s not wise to do so until about 45, when you can get all of the talents necessary to make you hit more often as well as do more damage while dual-weilding one handed weapons.

After 45, do whichever you please, however to stay elemental is still preferred. While you're not going to have hardly any downtime in enhancement at this point, you're still going to do more DPS in elemental, and therefore make up for it. PvP is easier while being an elemental shaman.

Above Level 50
Do whatever you want beyond 50, still. Enhancement is really good for PvP by now, and so is elemental, of course you may go recto if you want to heal for some higher level instances, because healers are going to be greatly wanted. You may even find yourself making money being paid to run instances in the outlands and Northrend.