If you keep your commander in your base after the first few min -> support com particle beam for the better eco
If not:
Jump com + machine gun + ablative armor plates (if on a hilly map where you intend on expanding or being aggressive with com)
Guardian com + riot cannon (if you think you'll be swarmed by raiders)
Radar is a good module to have on forward coms. It doesn't cost BP which means you don't have to stop moving to make it (aka you reach and build your mexes faster), and you don't have to rebuild it as it automatically 'updates'. It's less good with lots of hills, and less good again if you're not front-lining your com.
IMO the only modules worth more than 100m that are viable outside of extremely specific builds are ablative plating, and nanolathe. Ablative plating is good on the weaker coms that don't get as much HP, and can counter specific stuff like a wyvern or 3xraven trying to snipe your sup com (it will now need to do a second run). Nanolathe gives local mobile buildpower without costing buildpower itself, meaning you can use it to take advantage of reclaim fields more efficiently. It also gives "BP superiority" in a static grind fight, which can be a very big deal if you're intending on making a static push against an entrenched position.
IMO autorepair is a trap. It's efficient if you're moving your com in and out of battle a lot, but in that case the chance you get sniped is more of a concern than the efficiency with which you repair yourself (thus you would be better served by ablative). It's winmore.
Above is basically all you need to know in order to be using coms better than 80% people. There are more advanced things that are also viable, but they're less relevant. The majority of builds you see from other players are extremely inefficient. Less is more with coms if you're playing to win.
