Around 6”, not too thick, cut, well defined cockhead, slight upward curve, big cum filled balls, completely shaved smooth, and preferably attached to a cute young (legal) blond twink.
For what I want to have on myself: 7 inches and the same thickness it already is. For what I want to suck or fuck me: 4-7 inches and same thickness as me
Thin cocks are most ideal to me, and length doesn't matter. Girthy wider cocks have been harder to work with and enjoy I've never touched an uncut cock, but I look forward to trying one someday.
Keep in mind I've never done anything with a guy so this is all theoretical. Since I have no experience with guys I can't deep throat nor do I care to learn. So I would probably want something on the short side but thick so I could really feel it in my mouth. For taking it up the butt it would be a choice between something thick with moderate length to really stretch my asshole out, or slim and long so it can easily hit my prostate. But if you're a cool guy with a compatible vibe I'll just be grateful to play with your dick!