If you want to re-use the posts, you're probably best off with a chain. I keep dreaming of a way to pull the posts without having to get off the tractor and hook the chain to each. One way would be with some sort of hydraulic grabber, maybe a modified bale grabber? Another would be to bolt a V-notched steel plate to the bucket and pull the posts like pulling nails.
Hmmm. I suppose another approach might be to cut them off at ground level, pound the stub down a couple of inches and cover each with a bit of dirt...if the posts are cedar, redwood (hah!) or PT, they'd probably be good for another decade before rotting/sinking down enough to leave much of a depression.
BOB