I prefer not to use glitches because cheating can get quite addictive 
Then you can't ever use Incendiary Ammo. Or a Warp/Flamer/Incinerate/etc kit in a lobby where someone else is using Incendiary Ammo. Also need to stay away from using AP or Drill rounds when shooting at bosses that have a double/triple hit bug. And chances are, you've used the weight glitch without knowing it. There are alot of glitches in this game, many of them can be used unknowingly, and many of them have a fairly negligible impact on actual success (like the weight glitch). In any case, its an option to be aware of.
I've never used graal, venom or the gps after gold. don't they have low dps?
Nope. There are guns that out-DPS them- like the Reegar, Hurricane, Harrier, Raider, etc.- but they are all quite good in terms of straight up damage. But they have more virtues than that- Venom, for instance, has an area of effect. So even if its dps looks a little low compared to a ridonkulous crutch weapon like the Harrier, keep in mind that when you're hitting multiple targets you're effectively multiplying that dps, making it pretty incredible. And all 3 are great at applying ammo powers (incendiary, disruptor, etc.) and causing stagger (stagger destroys phantoms, can save you/teammates from syncs, and obviously, a staggered enemy is one that isn't shooting you... unless you're playing Geth, but then, why would you be doing such a silly thing in the first place?).