Faster, simpler and nicer to use, in my limited experience of ZSH. A focus on great defaults rather than expandability. But then I’m somewhat biased, having settled on Fish over a decade ago. ZSH might be better now.
Can you elaborate on "simpler and nicer to use"? The last time I've seen a description the differences, they were just minor simplifications of bashisms, like iterating an array, which don't simplify the experience significantly.
I switched to Fish about a decade ago too. "simpler and nicer to use" is a good summary, but to flesh it out a bit from my perspective: given how much time I spend in the terminal, the every day ergonomics are quite important to me. I used to use ZSH with oh-my-zsh and a bunch of plugins, over the years this got slower and slower, and the maintenance burden got annoying. It got to a point where opening a new terminal window would take maybe 5 seconds before it was ready to use. I tried Fish one day, and literally everything I'd customised ZSH to do came for free out of the box, no plugins, no maintenance. Startup time was instant. I now use Fish with a Starship prompt and I'm never going back.
The speed impact is one reason I've never liked oh-my-zsh and similar for other shells.
It's also why I love starship https://starship.rs/. Lots of plug-ins to customise what I want at the prompt, and all of it native compiled such that it executes in milliseconds.
Yeah, that great we have a lot of different opinion on thing and tools. For personal use i would try it. But for server side we as usual stick to default shipment, vim, zsh etc