Never
For PVP I'd rate the classes, from "Annoying as Fuck" to "Lol"
Defender (Titan) - Shield Bubble = ANNOYING AS FUCKKKKKKKKKKKKKKKKKKKKKKKKKK, especially in Control. WHY FUCKING BOTHER attacking a shield, everyone just hides inside it. Everyone in the shield can get a Defensive buff, or an Offensive buff, depending on how it is specced. Only countered by Bladedancer, everything else just bounces off the shield.
Gunslinger (Hunter) - Golden Gun = 3 one hit kills from afar, WTF
Bladedancer (Hunter) - Arc Blade = Tons of one hit kills, even can be outfitted to regen health on kill with Arc Blade. Invisibility not really a big deal.
Striker (Titan) - Fist of DERP = Blast Radius too strong. Can even survive a rocket launcher while using it.
Voidwalker (Warlock) - Nothing particularly dangerous about it, just a basic hadoken blast, can be stopped mid-animation because its SO SLOW FUCK
Sunsinger (Warlock) - You can self resurrect, big deal, not dangerous at all. I guess chucking mini-suns around is good chip damage on control campers, but you'll die anyway before you can pop 2 off in succession.