Well, I agree with the others that 2 racks of straight pool is tougher. Therefore the straight pool option should be more rewarding, in theory.
My situation is different. I ran 34 in straight pool one time, but there was so much luck involved it completely ruined the experience. I haven't gotten past the second rack in straight pool since then (several months). Its kind of like just firing a ball into the rail and hoping it goes in somewhere. If it does find a pocket, it is not really rewarding because it was just random luck and nothing more.
Every now and then I run a rack of 9 ball that just feels solid and well executed, as if I was in control the whole time. It is those racks that really thrill me. So at this point I will have to go with that as my answer. As I get better, I'll probably start feeling the same as other posters who appreciate their straight pool runs much more.