I moved from oh-my-zsh to grml ~10 years ago, and I've enjoyed it - it's got good defaults, is extensible (I've added custom stuff to handle how I manage directories for work things) and the single-file nature of the defaults makes it super straightforward to put it onto a new machine (ie a server) without then necessarily needing to do any extra tweaking

Yes, that's also what I use. Always found oh-my-zsh a little too much and too hipster-y for my taste.