My two choices would be either:
Flamer - as said, 4D6 damage against infantry, useful for setting fires or heating up an already overheated adversary, and no ammo explosion worries.
Medium Laser - only problem is that just 1 squishy bites it each time you hit (2 if they're in the open). Park at 5 hexes, and no matter whether they move forward or back, they're still in medium range, with no return fire.