In warzones melee teams will probably not work very well. In open world PvP they should be fine. Less obstacles in the way, ya you will get knocked around but if people have your back and are healing you should light people up.

Remember autoface only works in PvP if the ability is channeled or has a cast time and you begin casting WITH LoS.

For this reason I can say Operatives followed by Assassins will be easily the best melee based teams. Operatives have SOME range, fantastic self healing and insane burst. Assassins have plenty of utility, some range and the all important stealth (as do operatives) to get in close for the kill shot. Juggs and Marauders(higher sustained however) both have less burst than an Operative, slightly to much higher mitigation, better closers, but no real self healing.