For winning nebulae, you want a set of modules with multipliers against Light, Medium and Heavy. This usually means the basic three modules, although substitutions are possible (e.g. Rail Cannon for Needler). If you want to crack starbases (or the Ravenous Shadow) personally, you'll also need something with a bonus against Ultra-Heavy (Missile, Plasma Siege Cannon, Bomber Drone - Photon Lance might work too although it doesn't have multipliers).
Other than that, though? Run wild. Some things to try include Paralyzers (though they don't do well in nebulae), Insanity Inducers, Heavy Beam Cannon. One of these days I think I'll give the Zenith Heat Beam a spin as well.