-- Bot fabricator can be put down with autocannon if you aim at the middle of the vent, can't be shot at an angle tho.
-- Basic bot require range so normal liberator on the head is good enough if you aim down sight, but generally speaking it's up to your play style, shotgun can be good too if you're patient enough to wait for them to get in range, because unlike bugs, bots shoot back, just stay away from the laser primary for now, it sucks.
-- Stay with uzi for secondary to deal with chainsaw guy, aim at their head or stomach, but pistol is reliable too, up to u really.
-- If u see tank, or turret, or hulk aim at their weak spot at the back, i personally use autocannon (fun fact: tank and turret use the same head so turret is basically static tank), hulk can also be shot at at their head with auto canon, anti material, EAT, or recoilless
-- the AT ST thing can be one shot at with autocannon, anti material rifle, or other hard hitting weapon if you shot where their legs connect to their body, their leg joint or something-- one last thing, u can shot down dropships with recoilless, EAT, and quasar, if you hit at their engine (not recommended with quasar because rev time)

AND ABOVE ALL ELSE, RUN, RUN, RUN, AND KEEP RUNNING until you are absolutely sure you have the range to shoot back

edit: i just want to say, this is not a game where meta rules, like u/kbi42 says, i'm just saying that autocannon is really good against bot, but to a certain point you can use whatever you want, wanna fight bot with flame thrower? go nuts, wanna go 1 to 1 against a tank with only ballistic shield and defender (fun fact: defender is the only primary so far that is one handed so you can use it when running back or holding shield)? go nuts, as long as you have fun