It is totally up to individual preference. I wouldn't like going in the fall because I am not really into the Halloween decorations (nothing against Jack or Sally!)---and the weather can be randomly so hot and dry.
I love going the first week of December, because most of the rides are up and running, the Xmas decorations are in full swing, but the crowds (especially mid week) are still very low. The weather is perfect for me, too. The first year we went during this time it rained a little, which was wonderful because it kept the crowds down to the lowest level I had ever seen them. Anaheim rain is often very light and sparse. We went for 3 days, and it only lightly sprinkled two of the days, and besides that it was a perfect mild/cool temp for hanging in the park with some hot coaco. Loved it. Last Dec. we didn't get any rain, and the weather was sunny and high 70's.
Summers are often very hot, but the park stays open till midnight. I hate the heat, but love watching the fireworks in the summer at night. It is so nice to walk around in just a light jacket and breath in the summer air. The days can be brutal with the heat, but some people like that. All rides are typically up and running--but there is often one shut down for maintenance. Crowds can be big in summer, but go mid week to keep it managable.
Spring is nice--not as hot as summer. Just avoid spring break like the plague! We made that mistake one year, and NEVER will again. It was wall to wall people and we couldn't even find a place to stand for fireworks--even getting there 40 minutes early. Well, we found a place, but people were pushing and crowding us out by showtime and it was miserable. You couldn't even walk, and getting on rides was impossible.
We have gone almost everytime time of year because we go about 2 times a year (sometimes 3) for about 3 days each trip.
I thought it started early April. oops!!
