Hello,
I would say of the three, the pool at WL is the nicest, although the other two are not too far behind.
For ease of access to MK, obviously the boat ride from WL is the best, but the bus from AK might not be as bad since it doesn't share with another resort, although distance wise it's the longest. The PO-FQ bus shares with PO-R, and can add an extra 5-10 minutes or so due to the multiple stops, and can also be a bit more crowded at peak times due to the vastness of the two resorts. I have never really experienced bad bus crowds on an AK bus, other than right at closing time.
For access to MGM, both AK & PO busses are much easier than WL, which usually shares it's stop with another deluxe resort, usually Polynesian, but sometimes the Contemporary or GF.
I love the grounds at PO-FQ, and the river ride to DTD, and the fact that it is often less than half the price of AK & WL. The rooms at the two deluxe resort are slightly bigger, but not as big as those at the Polynesian or Contemporary.
Hope that was of some help,
Take care,
Bill