LibreOffice is pretty comfy and straightforward, has pretty much all the most important features right out of the box as well. The main issue and the most tangible difference about it is being based on Open Document format instead of proprietary MS formats. Of course you can still save, convert and work with MS formats, but they sometimes might get broken in the process (inappropriate fonting, broken geometries, broken animations and objects for presentations) while opened in actual MS Office suite. As for text and spreadsheets documents it's usually 1:1 compatible, presentations tend to get broken quite often while opened in something else - hence I always resort to just making static presentations and convert them to software-agnostic .pdf. WPS Office is also quite good and some devices these days come with it out of the box, it was also meant to be pretty easy to use, personally I was using it for a while on a smartphone and it was ok. The one I would discourage is Google suite, it's really terrible - not only because it's Google - but mostly because it heavily lacks even the basic features, to top that common actions (for instance upper index) are hidden behind some cryptic key shortcuts (no visual options available) that make even seasoned Vim users scratch their heads with how unintuitive they are. I haven't used other suites so can't give informed opinion on them. As for learning curve I would say that all, spare for Google's one, are easier than MS Office, it's just a matter of changing the environment a bit.
