At the low end, just get the jump on them with a big MB and kill them. If they berserk, keep dropping stuns on them and eventually you'll be fighting a commoner.
At the extremely high end, in many cases you don't have much chance unless you've trained your weapons well. Pull out all the stops. Fill your offense prediction pool and do a weapon prediction, use a CJ, get a commune, get ranger, paladin and WM buffs and give it a shot. Some big barbs can be MBed if your WvW stats are good enough, and some can't. Try a TV if you can't land MB.
