Very insightful thread. I actually do like the Google Keyboard because the predictions are so much more accurate and practical than the stock Samsung one. However everyone's comments have convinced me to try Kii and Swiftkey. I don't really care for the gesture typing much; I have small hands so using one hand to swipe across the screen of my S4 is pretty difficult. UI is nice enough for me but I agree it should be more customizable!
Also, I wish for emojis... Sigh... I downloaded the "emoji for English words" add-on dictionary but they don't show up :-( the comments say that you need to type the whole word, but seriously that defeats the entire purpose of emojis. They're meant to shorten words into one cute little icon, not make life more difficult for the rest of us by making us type the whole word :-( sigh...
But still in my case, I can't seem to select it as an input language although it says it's downloaded already. I don't understand why most Android phones don't come with emojis like the Nexus, or even the iPhone which has had them way back when. I know it's a shallow request but it's got a demand! Sigh, I shall wait for the day all phones will be equal with emojis. (First world problem much...)