Sorry, I was answering the OP who said they'd be at the end of September. For Raya, it matters which weekend she's considering at the end of September. The Monday without the MHP will have longer hours in the evening (10-9) than the one with the party (8-6). Neither will have evening entertainment per se (WoC will happen on both nights), but no fireworks or F! on either Monday. Still if they're only going to be in the park for three hours starting around 5, the Monday with the MHP doesn't make sense (because the park closes at 6:00 pm).
barbarann, next week is very different than the end of September. Next Monday is Labor Day, which is the last day of the summer season, the tail end of a marathon weekend, and part of a three day holiday. In terms of hours and entertainment, there really isn't much difference between Sat, Sun, and Mon. In terms of crowds, I'd guess that the largest crowds will be there on Sat and Sun because that's the prime portion of the weekend and the when the majority of the marathon activities happen. Still, I think you'll be in for good sized crowds on all three days.