More textures in the mouth, combined with more tabooness (mouth is very protected; it's a primal feeling, it's close to the brain, etc.). It's (usually) more wet, and saliva is an excellent lube provided there's enough of it (beats a dry pussy either way lol). The tissue lining the walls and pussy is very similar as well, so if any of you virgins wanna feel what a vagina feels like, the inside of your mouth is a decent approximation.
This all comes with a caveat though. My ex had a small mouth, and facefucking her was hard. The girl I dated before her had TMJ, and she liked getting fucked in the mouth, but honestly it always felt kind of awkward because I felt bad wanting to get my dick sucked by her since that shit is no joke lol. There's more stuff that needs to go right (especially when women have sensitive gag reflexes). I'm 7x5.3 and I usually have no issues with vaginal, but mouth is usually not the best since teeth and a small throat kinda hurt your dick. It kinda bends your dick, and since you're usually hard as diamonds when you're facefucking a person, it hurts after a few mins.
Good mouth: 10/10
Good pussy 9/10
Small mouth: 6/10
Dry pussy: 5 until you get her wet again
I never did anal cause fuck that unless she preps, and the first time I went to try I felt shit in her ass and noped out lol. In the future I'll probably just use my domination over her to force her to enema, then get her to like the psychological side of getting fucked in the ass, then keep it going strong so she doesn't stop with the enemas. I'm open to suggestions though, if any anon has a better strategy. Need me a bitch who understands how the prostate works as well.