I used i3 for several years and liked it a lot. I've recently switched to XMonad and I think I like it more. I find the configuration to be far more flexible, and the defaults aligned more with my natural preferences. My i3 config was pretty sizeable, but my XMonad config is (for now) quite small. Additionally, I found cycling tiling layouts in XMonad was a very useful feature that I never got from i3. Also I like Haskell, so that was a +1 for XMonad.