Dragon bone collection in wildy slayer cave best? (cannon, all diary, maybe void?, lance)>mythguild?

[spring river]

I need like 18000 dragon bones to max pray, my 3rd skill left until i max, thinking about doing green drags in wildy slayer cave seems pretty op, more than 3 spawns i think. thoughts? (hydra and vorkath are 50% efficient , not doing those)

[inner ledge]

there are 2 groups of 3 in the wildy slayer cave, and they're tankier
if you go east, just south of where old venenatis was there's like a group of 10 or 11 or something