Personally, I used TrueNAS Core (known as simply FreeNAS at the time) for my very first NAS setup knowing nothing about BSD-based systems, and it’s been pretty much fine. It has ZFS which is absolutely desirable for a NAS that you store important things on, and It has some quirks but Ive been able to accomplish everything I’ve wanted to with it just by looking up the miriad of guides available. Not saying it’s better than the alternatives, just sharing my personal experience.

However, if you’ve already got OMV setup and it’s working for you so far, I would stick with it. I believe you could always import your drives into another NAS system if you decide to move later, so why fix what isn’t broken?