Fastest prayer experience in theory would be Ourg bones burried in the wilderness with brawling gloves while having the chewed bone prayer bonus. 1680xp each, a full inventory would give you 47040 xp and take what? A minute to bury? Say 30 seconds to bank and get back to wildy that's 90 seconds a trip, 40 trips an hour, 1881600 xp an hour and that's on the lowside as it wouldn't take 30 seconds to bank if you did in the clan wars bank etc. so that's a probable 2m+ xp an hour and if you had a beast of burden too that'd save on the banking making it even more, probably over 2.5M an hour. Of course, you'd need to get over 224 chewed bones first, then turn them into pyre ships. And you'd need a few pairs of brawling gloves too. (To get an idea how many hours that would take, I've killed >4k mith dragons and had less than 100 chewed bones (I'd say around 80)). It's not a realistic scenario but it's still a load of experience theoretically possible an hour, not sure what altar/ecto xp would be but I imagine it'd be quite a bit less although a hell of lot easier to prepare lol.