Ported 90% of the time.
I have only ever really been happy with one sealed enclosure in my own car and that is 2 X 12" Realms with 1200 watts each powering them. The enclosure is a little bit larger than their large recommended but it sounds spectacular! It also hits high 130's too which ain't so bad at all.

 

Vented, But for me, Its not the space issue, I had to go sealed after a few months because it was killing what was left of my suspension , and my gas mileage haha.. but Its too late to go back, I cut up the existing vented to make the sealed... DOH !