I liked the windows phone keyboard, thought the Fire phone was okay, but am chronically unsatisfied with the Android typing experience. I have played with a few but settled for a while on Google Keyboard before moving onto Fleksy which isn't bad. Shame its broken for HTML text input fields...
The default Apple keyboard makes me incredibly frustrated, especially when used one-handed (which is 90% of my usage). No flow typing, and nearly all numbers, punctuation, and symbols are locked away behind layers of menus. I do find it the most accurate for typing in unpredictable plain text, but that's not very useful even for passwords (LastPass + most of my passwords have symbols in them).
Most of the third party keyboards are crippled shadows of their Android counterparts, but I can least get flow typing through them.
The Xperia Z Compact line is, for my money, the most pleasant Android phone I've found. The Z3C is still plenty snappy and is my personal favorite, but after sacrificing mine to the pavement deities the Z5C is still pretty great.