Lets face it its always a bit crowded although in recent years crowds have been shifting more towards fall.
June/July/August/September are hot hot hot and humid and rainy.
I've been once in June, once in July (second time coming up), a number of times in August, and a couple times in September.
Its really not too bad.
You sweat just walking from your room to the bus stop but then you get on the nice AC bus. Then you sweat walking from one attraction to the other but then in line you're either in AC or at least the shade. Then you sweat walking from an attraction to a restaurant and then you're in the AC while you eat.
I think there's enough of a balance that you're never too hot for too long.
We went in December this past time and it was COLD. I mean down right COLD as in my nose was frozen and I was shivering and needed to buy a zip up hoodie to wear over the one I already had on.
I'm glad I'm going in July this time lol.