They're both predictive typing, so they both fall on their face when it comes to two things. Proper nouns and slang.

Whenever I try to write one of those two thing (often, think email addresses, friends names , "yo", etc) I have to fall back on regular input.

With swiftkey, this means just going back to pecking. With minuum, it means going into a menu and switching to minuum's full sized view or long pressing each region to get a zoomed in view of the keys around there to pick out the one I want.

The compactness of minuum is great, though. And when I'm entering non-proper nouns it's as fast as any keyboard (given a few days to adjust).

I paticuraly like the "swipe left for space" function.

It makes me want to try even more radical keyboards. Maybe something chord based.