I used fish for around a year and a half and wound up switching back to zsh. fish's startup time is way too long for my tastes, and the devs seem completely uninterested in providing a "don't load plugins" flag. I open up new tmux panes/windows/etc all the time, so fish's slowness here is really noticeable. It also negatively affects using things like `tmux popup`, which spawns a shell. Things like this that take no noticeable time under zsh are sluggish under fish.