I do not like oil and hardly ever use it downstairs. The only oil-based lube I ever use down there (and it is NOT often) is "Yes!" Which is an all-natural, organics wonderful, safe, yadda-yadda lube. Lol. And still I only use it if I absolutely have nothing else. BUT it isn't that oily at all, so it doesn't freak me out so much as most oil does.

Oil cannot be shed from the inside of the vagina. It's not that healthy, so in my own opinion, water-based is the best choice.

One more thing, when there's long-lasting, plenty effective silicone lubes out there, oil is really not necessary. I guess unless you're doing anal and in that case I can't say because I do not do that -- I find it dangerous. Lol.

Maybe though, oil is preferred for anal sex because it's more thick than any other.

However, when it comes to PIV (penis in vagina) I think it's totally unnecessary. You have plenty of thick, super-long lasting silicone and water based lubes to need to use oil down there.