Buzz gave you some great options, here's a couple more.
Grab a bus to any of the All Stars, since these resorts are very close to the Animal Kingdom. When you arrive at the resort, transfer to a bus headed for Downtown Disney.
For me, personally, the best way is to just drive. The road from AK to DD is a straight shot down the road. If you can drive, that's the quickest and easiest.
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