Personally I always run outlaw for PvP but that’s because I prefer battlegrounds and other big group-on-group brawls where the mobility of Grappling Hook and Blade Rush really shines, plus having a ranged stun guarantees so many kills.
But for opportunistic, one-on-one WPvP like you’re into (that I don’t have the patience for haha), I think assassination is pretty much perfect. Wound + Crippling poison alone is a huge advantage and then you mix in Vendetta which is explicitly designed for one-on-one situations and your opponent is in a terrible position before he even realizes what’s happening. The cherry on top is FoK which means that even vanish+cloak is far from a sure-fire escape.
To be fair I’ve never really understood Subtlety since they changed everything and got rid of talent trees so I’m probably missing something there. But I think assassination is pretty much built for the playstyle you’re describing.