LSW - retard-friendly ultimate gun - in other words it does not requre as much strength as miniguns need, you can farm the ammo easily, range is quite decent and it does insane average damage.
Those FFA events pretty much confirmed there's nothing superior to it when it can't be outranged.
Plasma is worth mentioning due to it's insane damage and long range perk with max 24range - allowing very interesting builds.
Ofcourse if we would talk TC, I'd vote for Rocket Launcher, but this is general poll, right?
EDIT: just noticed you mixed some of the weapons that have little in common, plasma and laser rifles are like apples and oranges. And for plasma pistol one could honorably mention it, It's still insane damage, now in pistol package. Yet it's way too limited to pass the poll.
If you have a fav weapon I left out, feel free to mention it
You missed gatling laser, which can really be ... farmed ... yet we all know about it's uselesness...