It really depends on my mood. A lot of the time, the mood is killed if it's too playful with my girlfriend, but we don't have serious and passionate sex very often. When we do it is very serious and very passionate.
But it's not very... playful either. I mean... its fun, but I dunno. It's hard to describe, really.
I love it both ways! I have to say it isn't super "serious" and passionate very often but I don't consider that a bad thing. It's passionate in our own way but not the cheesy romance movie kind of way.
A lot of times, we have both in the same session. Sometimes we start playfully and end up getting passionate; other times, we'll start out hot and heavy only to have something make us laugh and get playful. They're both wonderful.