I used the free random faction and race changes on the Beta a lot just to see all races in action, and after that my choice for female Pandaren was settled. The only thing that I could stand apart from it animation wise on Horde is Female Troll. Every other race looked a bit off for my personal taste at least (Spinning Crane Kick usually being the "best" indicator, some races are hilariously wobbling up and down in the air while spinning on the spot).
If I were to roll Alliance, it would possibly be Dwarf or Gnome.