PvE probably the blade dancer, for end game content it's just too risky, closely followed by the striker. For PvP it's definitely the defender Titan. Just isnt offensive enough! If you could shoot out of it it'd be more useful. You know how when you come round a corner, spot a gunslinger and immediately backpedal around the corner? That's how you should react to three guys in a bubble shield! It should at least have a perk or exotic for it :)