I have to chose between 2 completely different experiences. Both are unique. I have a tiny penis and except for one occasion have never given a woman an orgasm with it ( other ways yes but not with my tiny cock) I managed to last way longer than anytime before or since while fucking her and she actually got off ( some have faked it but she swore she wasnt) I was with her for about a year after that and never even came close to repeating it.
The other experience was the first time in a foursome ( different girlfriend and a bi couple) Apart from everything else involved in the fourplay I was gently pressured by the two women into allowing the other guy to fuck me. He had never been a top before and I had never engaged so overtly with another guy.
I totally got aroused with the two girls watching him fuck me with his massively bigger cock. My little penis felt like clit ( and his gf said it looked like one in comparison to her bf) I almost came without my cock being touched then his gf put a couple her fingers on it and I shot a huge load immediately.