J.C.
I've been to both parks and would definitely recommend Hershey Park over Sesame Place. I think you should consider going to Dutch Wonderland though which is only a little over an hour from center city (closer to you than Hershey Park and will be fun for the whole family). Dorney Park is another great alternative you may want to consider. Also, all the parks will be significantly less crowded Monday - Wednesday. (I was at Hershey Park on a field trip about 3 weeks ago and some of the rides had over an hour wait although they were the big roller coasters...still it was a week day and school wasn't out yet). Have fun!!!