This quests is repeatable, it gives a decent amount of xp and reputation with Orgrimmar...

Very easy quests, as you collect the medals anyway when fighting in WSG...

In Warsong Gulch, the best classes to return a flag, are shaman, and druids (in most cases), this is due to the fact that they can turn into a travel form that will make them run faster and get back to their base easier than other classes would.
One VERY useful tip that I would like to share is a mostly secret spot on the easter part of the map. There is a very large tree stump, you cna climb behind/on this stump by continously jumping on the southern part of it between the stump and the wall of the gulch. When you get on top/behind it, you can hide and therefore not be seen by your enemies, this could be a great place to hide when you need to keep the flag hidden when your enemy has a great defense and a good enough offense that it could take your flag. Also, while hunters could be lookout for you with humanoid tracking, it is unlikey that they would look there, but if they came close enough to find you, a druid or shaman could be in a form that would make them not appear on their tracking. This is a good advantage and use of the enviroment to help win WSG.

Battlegrounds, and Warsong Gulch in particular, are much more dynamic than the PvE (instance) gameplay. For any strategy that you may put into use, a good opponent will counter you and force you to keep updating your strategy.

A great informative guide (and a general description of the battleground) can be found at:

http://wow.azzor.com/218/eppen's_warsong_strategy_guide.php

The biggest suggestion I can give for being succesful in WSG is to form a premade team with only higher level characters present. If you're in the 30-39 bracket, for instance, limit your group to 36-39. Just the presence of more higher level people will sway the odds to your side. Also, emphasize teamwork. A basic strategy followed by a group of higher level characters will generally win the match for you.