If you want to go mainly pvp and be dominant I would say go rogue/knight, simply because of the damage that they are able to dish out. rogue/mage has good control skills, a silence and root which would help a lot vs kiting and then rogue/scout because it was the old cookie cutter.
I play a priest/knight and the ONLY thing that can kill me are twinks that spend upwards of 40m on gear, maybe even close to 70m (all 8 pieces of used equip = VIII stat). My priest is level 33 and has about 3.1k hp fully self buffed. It takes me a bit of time to kill people that come at me, but I never die, the healing in this game is nuts. Think about healing as a viable PvP, priest/knight is ez mode against the imba melee classes in the game because of the HUGE defense boost they get. My priest with the knight skill (maxed) that increases defense by like 30% is over 1.8k.
Just my opinion.
Rogue/knight for melee dps
Priest/knight for healing/survivability (you're not going to beast anyone down in 3 seconds, but you'll outlast just about anything, and if you can VIII stat gear to twink PvP, nothing is going to kill you.)