Why not both? I use tasker to apply the preferred keyboard for the respective app. I have 3 different keyboards but I only use them for specific apps.
Missed this from earlier. I can't think of any specific app where I would prefer one keyboard over the other. As I said, I now prefer the aesthetics of Swiftkey, and I can only find one function that Kii has over SwiftKey. That function isn't something I use that often anyway, but it's also something that could potentially be used in any app. If I ever really want to switch keyboards, I can do that from the notification area.
I'm curious which keyboard apps you have installed and what you use each of them for.
Huh, I just found some more exclusive features for each keyboard.
Kii lets you swipe from a key to the space bar in order to immediately type the alt character, as an alternative to long-pressing.
After Kii auto-corrects a word, you can press backspace to immediately revert.
Kii lets you use third party keyboard themes (of which I've found none that I like, unfortunately), as well as more customization with text colors on the keyboard and even an option to use a custom background... but SwiftKey's themes still look better.
SwiftKey lets you delete an entire word by long-pressing on backspace.
SwiftKey lets you remove words from the user dictionary by long-pressing the prediction. Granted, this is less necessary in Kii because SwiftKey automatically adds things to the user dictionary whereas Kii does not do it automatically (when you type a weird word it will let you tap a prompt in the auto-predict space to save a word).
SwiftKey lets you undock the keyboard (which I never will).
There are also some different keyboard layouts between the two, which don't matter much to me because I'll be using the basic full layout pretty much every time.
I am suddenly very torn about which one to prefer... I think I'll go with SwiftKey for now because it looks prettier and the quick-delete is still a really cool feature. If I find myself typing alt characters more, maybe I'll switch back.