Georgina,
Hi! What a great time to visit Disney World! Seeing the Magic Kingdom decorated for Halloween and attending Mickey's Not So Scary Halloween party make trips in October a wonderful experience!
I've visited Walt Disney World many times over the years, and I've never had any trouble booking either online or via the website. Whichever method of booking you choose is truly a personal preference and will work great.
I know that many times when I am pricing out a trip, I like to use the online reservations via the "Book" link at the top of DisneyWorld.com. By entering in dates, resorts and ticket options I can easily see how each change affects the budget of the trip. Its also very easy to see the price per night of the hotel, and to view any
Special Offers.
On the other hand, if you'd like a more personalized approach with someone who can help answer your questions then a phone call works great! Also, I know many people do not trust online systems when submitting their credit card information, so the phone option may give you peace of mind in that regard.
Whichever method you choose, I hope you have a wonderful time this fall!