I like swiftkey a lot, because it's text prediction is flat out phenomenal, and far, far better than what the native keyboard does. Quite often I can type entire sentences with just the predicted words because it learns quickly how I write and what my phrasing tends to be. It's swiping isn't as accurate as Swype, but it is good enough that when I activate a 3rd party keyboard, it's SwiftKey 95% of the time. Only if I need to use one hand for a long time will I switch to Swype and use that.
However, the bugs are annoying. I don't mind the switch to the native keyboard in password fields (I'm glad Swiftkey can't log that), but there are two big things I want:
1) I want my iOS keyboard shortcuts to work in the 3rd party keyboards. I have a shortcut for my website's image folder URL, which I use often on photography forums, and it sucks having to either type the whole thing or switch to the stock keyboard to get the shortcut. I also have shortcuts for my email addresses, etc.
2) While all the little bugs are a bit annoying, the biggest one for me is the fact that often in SwiftKey, I can't hit 'submit' on a post in some situations with the keyboard activated...it changes something when looking for a predicted word or something. Sometimes a backspace will cause it to allow the button to reactivate, but other times I need to switch to stock to get it to work.
General iOS 8 complaint, though: What's up with the random loss of touch input from time to time when rotating orientation. It's not super common, but it's annoying.