I do not have a strong preference, but I am listing the reasons why I do not have a strong preference in case I am incorrect about any.
If LibreOffice required Qt5 / KDE Frameworks 5, I would prefer it to not be the default, and if LibreOffice required GTK, I would strongly prefer it not to be the default, but when I look through LibreOffice's dependencies, I do not see any GTK, Qt5, or KDE Frameworks 5 dependencies.
All things being equal, I would prefer to support KDE software and that means Kalligra Calligra. Two reasons I do not strongly prefer it being the default.
- The formatting ribbon is large, and cannot be moved, and my wishlist report has been ignored for years. I also noticed a duplicate bug report, also ignored.
- Last I checked, Calligra could not save in MS-Office formats. I might not like it, but most recipients of documents I send do not want to receive ODT/ODS format.
So, neither is perfect for me, so I would be happy with either as the default, assuming I am correct with the above.