Painsaw - A base destroyer. Period. Unless you're feeling damned lucky or you know what you're doing, you do not charge anything mobile with this.
Shotgun - 3-4 shots will kill a goon. Survive long enough and don't suck with your aim (or heaven forbid bring a combat buddy) and you're fine.
Lasgun - Plenty strong, but it's meant as a support weapon, so meh.
Mass Driver - VERY effective when you know how to use it, trust me.
Chaingun - Decent at killing most things, and tyrants and goons are big enough that the shots are a sure hit, and if you've ever charged a half-decent human with a suit and chaingun, you'd know that the chaingun is not underpowered.
Flamer - Also meant as a base killer, but yeah, it's a bit of a joke weapon. If they don't watch what they're doing, though, it crisps aliens damned quick.
Pulse rifle - Again, efficient base killer. Also kills bigger aliens quick enough if you can either predict their movement or get close enough to unload (while they're distracted or already weak, ideally).
Lucifer - Superb base killer. A direct hit with a charge shot will destroy about any base element but an Overmind, as well as goons and smaller.
I won't even go into the asinine teamwork junk earlier in the post. Surprise, surprise, it's a teamplay-oriented game. Cripes.