Many of us actually prefer 90 or 120 minute dates.
If, as was said above, you are looking for a slam, bam, thank you ma'am session, a 30 minute session will get your rocks off For you to leave happily. However, if you want to establish a rapport with your partner, and have more of a GFE time, then longer sessions are better.
I have always, until recently, gone for the 60 minute session. Unless she is well reviewed, I still make my first session a 60 minute session. But, if I truly enjoy her and her company, future visits will be longer.