if u PvE, frostmourne, both alliance and horde has the largest amount of guilds that raid heroic mode in south east asia. Can easily join a guild easily that has a raiding schedule that suits u.
U can pretty much PvP on any realm due to the cross-realm invite function and oQueue addon, check wowprogress for population and alliance : horde ratio, u dont want to end up in a dead faction or realm, dead as in no players, no players = no activity = no fun.

from my past experience, nationality doesnt matter since everyone in that game is mostly a prick, including myself.

have fun.