I'm a recent fish convert (from zsh) and I love it.
The only thing that annoys me is working with Android AOSP requires sourcing a bunch of bash functions that I don't feel like porting to fish so I'm occasionally required to drop into bash whereas with zsh and it's POSIX compatibility I could just source the bash functions and it would work fine. But fish's completions work much better out of the box and they have some useful features like being aware of your history in each directory.
The only thing that annoys me is working with Android AOSP requires sourcing a bunch of bash functions that I don't feel like porting to fish so I'm occasionally required to drop into bash whereas with zsh and it's POSIX compatibility I could just source the bash functions and it would work fine. But fish's completions work much better out of the box and they have some useful features like being aware of your history in each directory.