From what I've read, the other plasma weapons (Executioner, Initimidator and Tormentor) are better than the Opressor but I've only used the Executioner at this point, as my primary weapon in game (long range, good damage, easy to use, but not for everyone)I've hovering around the #30,000 mark for the past 6 months!
The Manticore looks nice. Does it shoot better that the one in the Training mission?
That one felt like I was shooting Coconuts with a fairground air rifle.
I do have some of those other weapons. I've just never used them.