I was there two Fridays ago on May 8th and we had a wonderful time. We took turns swaping the child and riding Summit Plummit first thing before there was a long wait and then enjoyed the rest of our day.
Nothing had longer that a 15 minute wait except one or two things and we just skipped them.
What I'm saying is, we found Friday to be a perfect day. I'd imagine there could be more local traffic on Saturdays, people who live close and head over just for the day or weekend.
Good luck with your decision.