Well that's a hard one to answer, it could be that time I slept on the beach covered in sand, it was pretty great except for the crab in my mouth, alternatively that time I fell asleep on a pool with the water covering my ears was pretty grand too, but by far I think the best one was that hammock in the forest that was between 2 trees in a clear space in the middle of the forest near an old shack that I rented, that was glorious like sleeping on air gazing at the clear star filled sky and that glorious full Moon, definitely awesome.
Coincidentally enough the worst place I've tried to sleep on was on the dirt in the middle of the forest, wasn't able to sleep at all and it lasted for 5 days, 5 days without sleeping and without food and out in the cold, though when I finally got home I slept so good that it felt like I suddenly regained my energy in only a couple seconds of sleep, turns out it was actually 3 day, felt like just seconds though.