If you are in a clan, I'd recommend pretty much any of the research weapons, since they are pretty decent, but they only unlock at certain ranks, and if you're not in a good sized clan it will take a while to research ( I practically built my whole clan dojo myself. Never trusting my friends to help again lol). For your secondary weapon, I recommend getting kunai or the throwing star things (I know the name starts with H), or if you can manage, kill the stalker and get Despair. The kunai are pretty good all around, but take a bit of getting used to, and the throwing star things are good against infested. Also, look out for events that give weapons, as those weapons often have a catalyst installed already ( but since I haven't played forever I don't know how often they're doing events)
Also, generally it goes Fire > Infested, Cold > Grineer and Electric > Corpus. This is just damage wise, so the different elements still have their effects.