I have 11 keyboards on my GS4 counting the stock ones. Swiftkey is good, but won't let me insert a "." in an email address before the dot com portion of the email address... as in firstname.lastname@example.org
. I can fix it after typing the .com portion, but I have to position the inserter to do it. And, no number row. I also had some issues with its word predictor/suggester.
I tried the Kii keyboard and happily purchased the premium version. I really like how it works.
Keyboards seem to be personal choice items.
I tweaked Swiftkey and per suggestions here, I changed the longpress to 200ms which helped deal with numbers. But found that if I paused too long trying to remember where to slide for the next letter in my word, I got a number instead. I never came close to being an expert on Swiftkey so there's probably a lot that I didn't discover about it, but I had times when the suggested words didn't work and I had to back up and hit each letter individually to get the word I wanted.
Kii has a floating word suggestion that is either distracting or a nice feature. I haven't decided yet.