There are so many “favorites” for so many different times. Orgasm, of course, as has been noted.
But urinating after having an uncomfortably full bladder for too long is a wonderful feeling, as is bowel evacuation any time that’s not, “OMG, not now!”. Climbing into a warm bed on a cold morning when you don’t have to get up—or at least not ‘right away’—is wonderful, as is climbing into a cool bed on a hot night, or finding coolness under the covers on such a night, when the spot you’re in is too warm.
Breaking a fast after a decent interval to build up one’s hunger, and eating something that one particularly enjoys, and even breaking wind when you find a good place (for you) to do that. I just hope that I’m not in the elevator with you when you decide that “now’s the time”. In that case, stepping off that elevator would be the finest thing in the world.