we've used them at the beach club and boardwalk before and they were fine.. we were having trouble with the one at the boardwalk to get it to open, and so we called the front desk, they talked us through it.. but, were prepared to send a replacement if something was wrong with it..
We flew into Orlando so we used the crib provided at the GF during our last trip and it was fine.
If you are driving to WDW you might consider bring your own, otherwise I would avoid the extra work while you are on vacation and use the one provided by the resort with a little extra cleaning prep they worked fine for us.
We stayed at the FW cabins this past May and the pack and play was in perfect shape. It was definitely on the new side. Mousekeeping brought us a few sheets so we could change them ourselves if we needed.