PvP? PvE? Ganker? Bomber? Straight-up dueller? Dungeons? Arenas? Trials?

In PvP magblades kinda suck compared to other classes. However they are getting some minor buffs this patch so that's good. Also they are buffing war maiden by a lot and it will be very very good on magblades since all of their magicka abilities deal magic damage.

Best for vMA? No, not for me. I'm a PvP magblade main, but I mostly take my magplar into vMA. I'd probably also take a stamsorc or pet sorc before magblade or even my stam DK personally. I can't speak to what's best at a very high level of proficiency, but in terms of ease of use I find magblade surprisingly lacklustre. That's despite a bunch of favorable factors, such as healing while attacking (Swallow Soul, Sap Essence, Siphoning Attacks) having a decent ground DOT (Twisting Path) and being ranged. I go into vMA with PvE gear and PvE skills, though as a PvPer the one thing I haven't tried is Dark Cloak. Then again I'd argue that Shadowy Disguise is a useful skill in vMA. Though I don't normally slot it, you can use it to shed aggro from "Taking Aim" archers, if you get caught in a position where you can't interrupt or kill them immediately.