I'm totally versatile though tend to switch from mainly bottom to mainly top depending on.... well, who knows?
When I bottom, the act of raw penetration always gets me hard as a rock, whether I've been hard moments before or not. I then stay rock hard throughout the fuck, whether it takes minutes or more, and as often as not cum without touching myself - though I do try to stave it off until I have my top's load deep in my gut. And incidentally I much prefer to be on my back, rather than doggie.
And when I top I love to see my boy hard from the outset: I love it that he's turned on by the anticipation of having my cock in him, and by the penetration itself. I want him to writhe with pleasure as I fuck him and love it even more when he shoots his first load during the fuck