Been using fish for awhile. I don’t need much more than smart autocomplete (which is built in) and some small QOL plugins. Sometimes it sucks because the syntax is slightly different than bash or zsh so you will have to get used to that.

Don't know how much "minor customization" is to you, but perhaps try adding some major stuff before giving up on it. Personally I started with prezto, customised it, and added a few things like fzf. Fish is probably nice too but I haven't got around to giving it a fair try.

Both are good (and Bash too). Try them all and choose the best one depending on the context. For example, on my main PC I use fish with a few plugins (and fisher as the manager), but I'd never use it on a server due to it not being POSIX compliant.

I use zsh with prezto plugins which makes it behave exactly like fish, except it works with batch scripts. It's perfect