I personally hate 69 in heterosexual relationships. I have not had the opportunity to 69 in a same-sex relationship, but I imagine I'd enjoy it a little more.
Blowjobs take a shit ton of work and are painful in 69 (and I CANNOT be under a guy giving him a BJ-- I am so claustrophobic it will make me go hysterical). I imagine it would be easier to 69 with a girl, but Idk...
69 just seems sort of ridiculous to me. I want to do a good job when I'm down there-- blow their mind. If they can still focus on giving me oral while I'm doing my thing, then they can't be enjoying what I'm doing *too* much.