To put it straight:

71-80 AV = 18k xp per bunker/tower cap and 180k xp for a win (loss is around 80k)

Questing = 22-25k per turn in.

What this means is, given that both main towers (Dun Baldar for Horde and Frostwolf for Alliance) and the 2 main towers/bunkers prior that allow the generals to be without buffs, you are set with 72k xp. Tower/bunker caps will give you roughly 3.13 quests worth of xp. Losing gives you around 3.6 quests worth of xp and winning will give you around 8.18 quests worth of xp.

Total: AV win with all bunkers/towers: around 11.31 quests worth of xp.
AV loss with all bunkers/towers: Around 6.73 quests worth of xp.

Keeping in mind that an AV lasts about 15-18 minutes and also keeping in mind that you don't get xp from kills (unlike questing), I have to lean more towards doing AV grinds. The extra honor and marks are a plus and, should you choose to PvP later, the honor is a great way to start your 80 with a few pieces of welfare PvP gear.