There's also the case when you aren't in an AT-AT. Only 1 person can drive it, and I usually play as a shock trooper anyway. If an AT-AT exists, I can get in 2 or 3 solid hits on a snowspeeder if I'm lucky, and by that time, the AT-AT is dead. There don't seem to be very many people who play shock troopers for some reason, but even if there were more, all it takes is another speeder or sniper to take care of infantry on the ground.
I suppose the answer really is more organization on the imperial's part, but I'm not sure I have time to join a clan, and that would just mean the rebels would be that much more organized as well.
I still think hitting the snowspeeder in the back with a missile should detach the tow cable. I'd probably be happy with that
Or maybe 2 missiles... the back of the speeder should be sufficiently messed up by then. (Although it'd be awesome if gunner died like in the movie, and the tow cable didn't get detached when the walker went down, and took the speeder with it... haha)