[aaxa]

I prefer Hammerspoon to be honest. It's free, open source and you can modify pretty much everything on your Mac. Be it key bindings, hotkey sequences or automation of other software's behaviour and so on.

[bartvk]

I use 'em both. Hammerspoon is amazing, however Karabiner nowadays has a nice GUI for remapping your keys. This makes for an extremely low entry.

As an aside, the original Karabiner developer has a donation page here: https://pqrs.org/osx/karabiner/pricing.html