Ultimately, which keyboard seems "most suitable" for a user will depend on the user's peculiar requirements - which, from experience, are usually little understood and rarely defined.
There have been a few references in the DC Forum discussions to the Microsoft product
SwiftKey (MS apparently bought up the company several years ago.)
I only recently started using a smartphone for my own purposes (though I have set up smartphones for other people to use for at least a couple of years), as there is some functionality available that can't so easily be utilised via a laptop, though I do use an Android emulator on the laptop so that I can mirror the Android device's system on the laptop. I plumped for a refurbished Samsung Galaxy S7 with the Google keyboard. Very good. It was a no-brainer.
But it was whilst I was setting up a Japanese and a Thai keyboard for a couple of users that I started to research and experiment in earnest with other keyboard apps than the obvious ones mentioned in this thread (above) and which are otherwise very good.
That's when I stumbled upon
SwiftKey. I was initially
very skeptical (because it was a Microsoft product, after all!), but, on reading user reviews, I couldn't find a single real criticism - it was mostly all positives. So, rather than get the other users to be guinea-pigs and experiment with this unknown app, I tested it out pretty thoroughly on my own smartphone first.
Because I tend to be rather critical and see all the warts in things, I have rarely been blown away by any application's functionality and potential - sadlement, they are nearly all defective in some regard.
Not so
SwiftKey, it seems. After trialling it, I subsequently installed it for the other users, and they too were blown away by it. The hardest part was getting them to actually try it out in the first place ("suck-it-and-see"). The built-in
ergonomics and predictive and lots of
other functionality in
SwiftKey seem to leave most of the other keyboards standing in the dust.
Well worth a try, I'd suggest.