Simpler interface but lacking more advanced features of MS Office or Libre. It has the features 90% of users actually use though.
Nearly perfect DOCX formatting compatibility. The only thing I have ever noticed when collaborating with Word users is the bullet symbols on list items may be different on my end.
Onlyoffice sucks very bad with macros in my experience, lacks some advanced functions, and infuriatingly doesn't seem to have options search, but other than that it's fantastic, very intuitive, ergonomic and sleek option.
You might also find the Python library pandas useful. Its “DataFrames” can mirror your excel data 1:1 and you have convenience methods like to_excel(). Easy to combine with numpy for performant matrix math.
XLSX just becomes a container for storing/sharing your data, and while Python is used for analysis. I would use matplotlib for plotting rather than embedding in the sheet.
Glad to see someone mention OO. I was going to, and saw your comment. I will always be down for LibreOffice, but OnlyOffice might be the "best" option for lots of people that are easily intimidated with change (or more specifically how something looks different). Even if it is lacking on some features, it just matters how the person it is recommended to uses MS Office. Being fair using MS Office or any of the similar suites is overkill for what they do. If smaller programs like Wordpad (RIP) or opensource Rich Text Format editors could handle so many general purpose documents.