Hmmm, makes me wonder if it's uncut guys who don't enjoy a Venus 2000 as much. Pretty sure nit's the stroking of the liner on the tight skin that feels so good for me.
Vaseline was my go-to when I was a teenager, even though it was a pain to clean up and left a slick veneer on the walls of the tub. It almost makes me blush in retrospect - it must have been so obvious to my parents what was going on in those long baths. These days, I mostly just use my hand. When I masturbate in the shower, I use soap. When I have time for a nice long session on my bed, a bottle of olive oil on the bedstand keeps things feeling spectacular.
I find cum itself makes awful lube. I've squirted some out while edging. I find it becomes watery quickly when stroking and even ruins the lube I'm using. That's my experience.