What is your preferred weapon to upgrade the AT-ST with?
Best weapon on AT-ST?
I've only tried the light cannon, and was underwhelmed. I've been meaning to try grenade launcher+mortar since heavy cover cut so heavily into the AT-ST's damage, but I didn't want to bring it to the recent operations, and the need to move more is a concern.
I always put on light cannon to beef up the dice from the main gun. You have a pretty good shot of killing or disabling AT-RT's with a single attack!
I also use the Mortar quite frequently to slow enemy troop movements and to selectively panic troopers off the board or off of objectives if they get too far from a commander.
Have not used the grenade launcher much, but as my table becomes more cluttered with buildings and terrain I will probably be trying it more and more for close quarters fighting.
ALL THE WEAPONS!
- GENERAL WEISS
- GENERAL VEERS
- HQ UPLINK
- MAXIMUM FIREPOWER!
The range 2 shot of 3 red, 5 black, 3 white with ignore cover is a game-changer, and the mortar almost always has something to tickle at long range. It does paint a bit of a bulls-eye on the model, but since it's rarely a scoring unit it doesn't have to make it to the end of the game.
I usually place two weapons, mortar plus one.
The mortar is my mvp for sure over all my games. Really slows down enemy troopers when they’re always only taking one action. 
I find that I rarely catch things in r1-2, so the twin blaster is the next best hardpoint for me. Mostly, the walker serves as heavy area denial and long range arty to keep folks away from things I care about, while my stormtroopers fill in the ground space and seal that territory as mine.
I agree. I don't see enough stuff in Range 1-2 for the grenades to be that useful, and I don't find I get that many uses out of Weiss. So Mortar or Light Cannon for me. This also keeps it a bit cheaper, although that's a hard word to use with this. These things can dominate a board space even without a lot of upgrades. I don't know that I've ever seen enough stuff in front of it to justify Arsenal 4.