Well it depends on what you want to do when you get there.
Do you want to see the holiday things, the fall things, mostly go on rides, or see shows?
We prefer July. Yes, it is hot but I don't mind the heat. The parks have longer hours. Socal APs have been blocked by that time. All the shows are up and running. There are crowds but it isn't nearly as bad as when we went over the holidays. First thing in the morning is very nice. And with good use of collecting fastpasses we never wait in a line longer than 20 min, but are able to get in a lot of rides in a day.
Next year we hope to get APs again and try out going during the Fall if they have the Ghost Space Moutain again. I expect it to be crowded based on what I'm hearing now, but like over the holidays, we lower our expectations about what we can ride.