Ultimately I found PVP in the game to be boring and often times annoying, I feel like they tried but really missed the mark on it. For the long run I would have to go with Bloody Bay because those Shivans were just so freaking useful, but I do have a couple good memories from Siren's.
I remember early on I was able to use Stealth as a Mastermind and go ontop of a little ledge right above the Hero entrance. I would sit up there and rain pets down on people (they would get killed by the drones before they would do anything but get some attention) and people would tear the place apart trying to find me, never checking that little ledge. Once they stopped looking I would repeat it, just for laughs. Sometimes I would have the pets start dancing before they got zapped by the drones.
Of course it was things like this that made it so extra drones were added RIGHT on the ledge, and drones were given higher perception ratings that they could provide to nearby players as well. Still, it was silly and fun.