Haven't done October yet, but have done high season middle August, end of August, beginning of September and middle of September. We're attempting an October trip next year, flying out the last Monday of September and crossing over into October.
There are two things that will be majorly different between August and October - the temperature and the crowds.
American schools are out June through to Labour Day, so August they are all there. Then of course, the British schools are July to beginning of September, so we're all there too. I should imagine there are quite a few other countries around the world that observe the same school schedules. So it is busy, queues are long, even with fastpass, and parks that you could get around in half a day become dragged over 2 days, because of all the waiting. Everywhere is busy, the counter services, the restaurants, the shops...
People, people, everywhere!
October will be our half term, but I have a feeling Americans don't really do 'half-terms', they tend to get random days at the end of their semesters, and then big things like Thankgiving/Christmas/Easter off.
Looking at the 2010-2011 school year for Orange County, it looks like there's a day off for them on 15th October, and then they don't finish until the 28th October, and go back on the 1st November (just one or two days off). So, locally at least, you should be good!
Free dining almost doesn't come into play now because of the credit crunch it's difficult for anyone to go on holiday, so this year at least, it's been offered to UK people from August through to December (if booked before July) through DisneyUK, so while
DDP does bring in extra people, it shouldn't be too much of an issue for you in October.
And the temperatures will be considerably different too. I don't mind the heat and humidity, but my mum and especially sister, are terrible in it! I think last year (September only trip) was the first year that my sister didn't try to faint on us due to the temps/humidity, which is saying something.
Unless you are up for waking at the crack of dawn and being at the parks for rope drop, returning to your hotel for the best part of a day, and then heading back out again at night, then October is better. AK is the worst park in those temps. I refuse to stay in AK past about 11am, and even then it's a push, so we barely got to go there when we did August holidays!
We've also found out August holidays (and beginning of Sept) to be plagued by the normal mid-afternoon torrential downpours! They seem to lessen the further into October you go, and I guess October is even better. They only last for an hour or so, but they do tend to bring a lot of outdoor rides to a stand still!
The other thing is August/September are busy months for hurricane activity, but the further into September/October you go, the more you find that the hurricanes start to travel southwards of Florida and become less of a problem - instead, as they sweep past Florida, they take all the rain clouds and make the temps in case!
- according to our DVC guide!
Soooooooo, the point of the post? If you have a choice between August and October? Do October!!! Flights will be cheaper, hotels will be cheaper, and hotels/parking should be cheaper over here too, to get you to the airport!
Really depends on the cash situation...
and can say that each time, less crowds than August and a much nicer experience than in August!
