There's also the Darkmoon Faire for heirlooms if you're patient (or have a lot of alts/multibox).

Level 80 shoulders/robes cost 2,175 jp, 60 champion seals (can't upgrade with this currency), or 110 darkmoon prize tickets. So one champion seal is worth about 36 jp, and one darkmoon prize ticket is worth about 20 jp. Other slots/upgrades have similar ratios.

Mirai has commented that as a tank, 3-4 days gave 70,000 jp. I'm not sure how many hours it was each day, but this is the fastest way to do this outside the game as there's no limit on how many times you can do this in a day or month.

When I farmed the Argent Tournament for mounts/pets, I only did the quests (14/day), and it took 20 ish minutes or the equivalent of around 1,500 jp/hr. By comparison, this would have been more efficient for Mirai if his 3-4 days was at least 47 hours or so. Likely not faster than a tank queue. Also, there's a daily limit, and you'll need a different currency to upgrade them.

The Darkmoon Faire allows you to trade gold at the AH for 55 prize tickets at level 15 and 80 prize tickets at level 85. Also, the profession quests give up to an additional 20 prize tickets. There's also a quest to kill 250 mobs for 10 more tokens, which is a nice bonus to regular play (adds 0.8 jp/mob).. The turnin and profession can be completed in minimal time once a month. Translated, these are worth 1100 jp at level 15, 1600 jp at level 85 and an additional 400 jp if you do all the profession quests. Doing a round of the darkmoon dailies would net an additional 5 prize tickets (100 jp), but in my opinion takes longer than farming the jp in heroics (or the argent tournament). This method does take a while outside the game as the quests are only monthly, but it's the most time efficient inside the game by a wide margin (turning in the item quests is easilly less than 5 minutes, or 15,000 jp/hr, the profession quests take another 5, or 5,000 jp/hr when doing those).