Seems like the ally win bgs that are more pve oriented, anytime they actually have to engage another player they fall apart. Healers are never targeted, I don't how many times I've seen people go after the hunter and not once touch the 2 healers behind him who are free casting. They also never protect their healers well, unless the healer is saving themselves, ally will not help the guy out. Of course this is anecdotal and I don't have real stats to back anything but this is what I've noticed when I pvp <shrug>