Especially if you go every year, the AP is the ticket to buy! You can get two trips' worth of use (e.g., one year: end of a month; year two: beginning of that same month).
And remember, DVCers get a discount on the APs, which make them even more cost-effective!
As others have suggested, if you can plan 2 trips, with a TOTAL of 10 days or more of admission, within one calender year, I'd go with the AP.
If you just can't swing that....we've bought our tickets from undercovertourist.com for the past 3 trips. If you're a subscriber to the mousesavers newsletter (at www.mousesavers.com), you'll get an additional discount via special link in the newsletter every month.
Definitely APs! With the $100 discount per ticket, it can't be beat, and if you can shift your annual trip by a week the second year, you can get two trips on one AP. We did that for quite a few years, but now that we get the discount, we tend to make 3 trips and not worry about shifting.