Past 60 it isn't worth trying both sides (esp TBC where both sides are EXACT mirrors of each other). While I have heard Allience get a special viewing of the Lich King early in the WOTLK, overall it wouldn't matter considering the times Lick King spams you saying how you are in his plans and that he will have his revenge (ya, I'm insulting the whole, "feeling closer to the big bad guy of the game" thing, when I actually saw Illidan yelling at me I was impressed and was liek WTF I PISSED ILLIDAN AFTER ALL MY HARD WORK, but having Lich King is most areas/dungeons yell at me just for doing something minor kinda gets bland and meh).

But yer, I'm the type to try different alts on both sides when I have spare time.