I used Thunder for a long time, but I have been giving Arctic a try lately and like it. I will likely give Mlem another shot after the next update. Voyager is another great one, but I have not used it for a while.
Overall, there are a lot of great Lemmy apps and I love that most of them did not get abandoned after the initial wave from the Reddit exodus died down. I think we have more high-quality Lemmy apps than there were for Reddit.
LibreOffice and OnlyOffice are both compatible with MS Office formats. LibreOffice is more popular, but OnlyOffice has better compatibility with MS Office files and the interface is very similar as well.