The Disney World App looks like a great companion to navigate the parks, but ofcourse you need internet access for it. I was wondering how good the wifi is at the resort, both in the park and the hotels. Is it slow sometimes? Is it widely available throughout the resort or only at certain areas?
Or would you advise on getting a local data sim card and if so, any suggestions to which operator and where to get it?
Personally, I wouldn't even call that app a great companion, I'd call it a necessity.
You can do a fair few things from the app, which saves you looking for Kiosks and such. My last visit was in May 2015, and honestly, I wouldn't leave the resort without a charged phone to have access to the app.
The park-wide WiFi at Disney World is probably your best bet, it's pretty speedy, not great, but plenty for the app itself (managing fast-passes, reservations, wait-times etc).
The resort WiFi is generally pretty good as well. Enough for some YouTube streaming and stuff like that.
Can it be slow sometimes, yes, though that will depend a lot on the crowd level of your location. As for availability, I believe that each resort has full coverage, as do all the parks. Reception can be spotty in some places in the park, but that's usually indoors under a lot of concrete. Overall it was pretty good in my experience.