well...not entirely true. they all can kill the atpts depending on if they go back around for another pass or not. this is how i attack:
I destroy the first tank droi in site, then i destroy 2 of the turbolasers on my way to the atat by the atpts.
Then when i get ready to launch tow cable, i make sure to kill a few stormies, then i launch the cable, and take down that walker.
As soon as that walker is down I head towards the walker by the shield generator and on my way i take out the turbolaser on the right and the barracks behind it and the turbolaser on the left and the barracks behind it. Then I take out that walker.
Immediatelly I proceed to the last walker, on my way i destroy the 1 or 2 left over turbolasers, and then i launch tow cable, and hear 'the gate is down repeat the gate is down' and i take out that at-at.
THEN on my way to the bonus powerup i take out the one turbolaser that was placed lower than the ones on the canyon. I then destroy both turbolasers up by the powerup as well as the barracks that the turbolaser is in. I pick up the bonus and turn around and go towards where the tank droids will show up.
I then head down and take them out from behind.
When that's done, i take the ones out that are on the other side of the canyon, trying to aim ahead of them so my shots hit them.
Once those are destroyed I usually destroy 1 or 2 tank droids that's near where the tie bombers show up.
Then I destroy the 4 bombers, and try to take out the rest of the tank droids.
Then I turn around and quickly destroy the last wave of tie bombers, which is really hard since they go pretty fast, i usually end up going head to had with them.
Then once the tie bombers are destroyed i go immediatelly to the shield generator and destroy it and all the tank droids that uncloak themselves around that area and i deastroy that barrack too and the snowtroopers that are around that area.
THEN I go back to the first walker i knocked out and finish off what's left of it, and the snowtroopers, and i destroy the snowtrooper's home (the barracks)
then i go to the weapons factory and destroy both missile turrets usually one spots me b4 i can shoot it down, and fires a missile, which someitmes hits me right when it dies.
I then destroy the barrack that is there and the 2-3 snowtroopers running around saying 'we're free from the shield YAY!!!!' and i finally finish off the shield generator, which i usually end up doing 10 seconds after atpt reach landing zone.
That is how i get the job done, and i get gold that way AND i get extra kills and stuff.
If you're lucky you can shoot that barracks near where the raptor transport picks up the atpts.
Also, wanna see something VERY freaky?
when you start out, immediatelly go to your right and see the at-at which is stepping in the barracks! AAAAHHHH!!!! it's a holigram that can be destroyed (the barracks that is)!!!!!!!!!!!!!!!!!!!!!!!!!!!!!