Some quick math and runs out at great cleave have produced some XP/Min stats to help you decide how to best spend your time raising your PVP scores.
Fort Cap – 1000XP Time to complete on average appx 17 minutes. Comes to appx 58XP/min
GC Missions – You basically run 3 missions and 3 missions (Vanquish will be in one set). So, every other run you’re going to carry vanquish so the next set you get the full 3 non vanquish missions. To do a full set of 3+2 it takes about 11 minutes. This results in appx 105XP/min 350+200+200 and 350+200. Higher if you were to not lose time and get 5 tokens for vanish, but that’s not generally going to happen.
The difference though between the methods is one is a treadmill while the other can be a rocking chair.