I don't think Vincent would be particularly adventurous as a lover but is very generous, as is in accordance with his astrological sign, like so much else of his personality is (being sensitive, not wanting to make waves, etc.). He is well suited to acquiring bedroom skills and performing them well, since as a Libra he is very concerned with being well attuned to his lover's needs, but being the shy romantic that Vincent is, I put him in more of the "traditionalist" category of wanting to wine and dine his lady and "make love," and would probably need some coaxing to engage in anything rougher or kinkier if that was what his partner wanted. Vincent is all about wanting to make the other happy.
I like to be in the "they slept together at least once" camp, although admittedly more because I want to be there than because I think there is any particular logic that says I should be there. My headcanon is that they slept together exactly once, which was the night before he found out that Lucrecia worked with his father, and everything fell apart at that point. The only foot I really have to stand on in arguing that they could have slept together is that he canonically proposes to her and it's my personal belief that you don't propose marriage to someone you've never slept with—that, and if you look at the four flashbacks that take place from their meeting to this scene, you can see a progression of him becoming more comfortable with talking to her, touching her, etc.—but I really prefer
not to argue it because it's all very subjective and I have no true conviction in it. Much like my relationship with religion, actually, which I also don't argue.
Lucrecia, however, as a lover, would be a bit more...interesting, especially post-fucked-up-shit-in-which-I-donated-my-body-and-sexuality-to-science, which is where my headcanon tends to live. I think that sort of thing is likely to have an effect on one's relationship with sex and I like to write Lucrecia as trying to seek a thrill, tying into the self-destructive tendencies that she has displayed in canon. Between Lucrecia and Vincent, Lucrecia would definitely be the more sexually aggressive of the two.
Plus, Hojo in my headcanon was just all roughness and selfishness and just objectifying her for his own needs, and she's had to deal with that, so. But whether that would be in her past, present, or future depends on which part of the timeline you're considering.
Actually I just wrote a fanfic on this which I shall shamelessly plug now:
Anomie Theory 
However, it is firmly my headcanon that Cid and Shera are engaging in a secret 24/7 BDSM lifestyle. In which he humiliates her in public, but she actually dommes him and punishes him later for all his bad behavior. *nods slowly*
