It takes up two slots but I like taking autocannon and using flak as my main. When tripods show up I will call down a commando, break their shield with the cannon then hit them with commando rockets. It's been working pretty solid for bringing them down and giving me lots of anti-air/crowd control.

I'm going to try a similar loadout with grenade launcher and eatit. Again, the issue is taking two slots but it's dependable and the first one is definitely versatile.