i take an opinion beside all the "play what you like"-Guys.
If you need an answer: Alliance or Horde, i stay with the alliance.
Reasons(and all the following are all just my opinions):
1: In 40man Raids Alliance is superior (i repeat: all just my opinions). I dont want to start the whole Paladin or Shamans discussion, my feeling is and always was, Paladin Blessings (if you got 3 Paladins or more) are stronger than Totems. This and dwarfes Fearward.
And 2nd: Location Location Location
. We will start with MC and Onyxia only. Later we have BWL. The first 6 months to a year , the Blackrock will be the centre of the World (of warcraft).
And even after that. ZG is very reachable from Stormwind (also the Yojamba Island for Hakkar Head Buffs)
When you playing Horde you are sitting in Orgrimmar.... yeah , everything is only 5 minutes Airship and 10 min. wyvern away.
But that was just my Opinion man.