I'd say penetration, because if you're a male, you can better control the rate and everything, considering that some girls suck (no pun intended, lol) at giving blow jobs.

Doesn't that let you down, guys? You know, when it's just not doing anything for you? There was this one girl, who was living with me for a while, and it was a serious relationship, so at first when it was terrible, I felt comfortable in telling her she was doing it wrong, so we worked together to find a style that was amazing for me, lol.