Very good comments above. I had a Fire tablet years ago, liked it well enough for what it was. But I moved on to an iPad and have never looked back. The Fire tablet is a niche item. I find the iPad mini is an unbeatable all-round tablet. Among other things it's my main choice for reading my Kindle books. The Kindle paperwhite gets so little use I'm sorry I bought it, but it is easier on the tired old eyes especially for late night reading.
As others have mentioned, I don't expect to be able to download books while on airport or other public wifi systems. If I can, it's a bonus, but I wouldn't expect it. Same for hotel wifi, unless it's a premium wifi service I've paid extra for. A couple of years ago my hometown hub, DEN, had the fastest airport wifi, but in 2018, Seatac knocked it out of first place, according to this article reporting on the fastest US/Canadian airport wifi systems as of January 2018.
Cj-traveler, thanks for the tip about turning off wifi on the Kindle if I take it traveling. I hadn't thought about the loaned-book issue. And, Doug, I agree: "I just can't imagine traveling without an iPad/iPhone or Chromebook/Android phone." In my case, a foot firmly in both camps, I have my iPad mini and my Google (Android) Pixel2 phone (with Google Fi mobile service).
Anyway, phred, I'm sorry about your bad experiences with the Fire tablet. Some of it sounds like weak public wifi networks, and it's hard to know why the tablet didn't connect in other situations. Did you attempt to research the issue after you returned from your trip, to pinpoint the reason(s) for the problems?