I played alliance on 2 servers and horde on 3 server... different battlegroups in EU.. and I have to say.. sadly alliance seems to lack all skill overall :P There ARE exceptions.. but so there are on horde side ^^
Which side.. I haven't decided yet.. atm being casual I play alliance with some friends and don't care much about progress/success. Might change with wrath and if I ever raid serious again only on horde side