I am not using zsh, instead I divide between shell scripting in rc and interactive usage of fish.

I like rc for these reasons:
-it's small-I used to do a lot of sh scripting and learned all of rc in two hours
-it's not backwards-compatible-I like it if people are brave enough to throw old ideas away and learn from the earlier design mistakes
-one big advantage is the way shell quoting is implemented. When I look at this page (http://mywiki.wooledge.org/BashPitfalls) most of the issues are quoting errors. Rc has very simple quoting rules and avoids this kind of errors in a very elegant way
the quoting rules are:
text is quoted in single quotes 'abc'. if you want to quote single quotes, you write a double quote, so '''abc''' expands to 'abc'. Variables are expanded into their whole content and treated as one single string, so
a='this file'
rm $a
does not remove this and file, but 'this file'. To save multiple variables, you use a list:
a=('this file' 'that file')
touch $a
creates 'this file' and 'that file'.

Fish on the other hand is like a zsh with less/no configuration and also a non-standard syntax. It has syntax-highlighting and quite good tab completion.