Neon seems ideally positioned for KDE-specific development. Latest KDE frameworks but not necessarily the latest Ubuntu base.
While KDE neon is great for casual users, contributors will find KDE neon excels. Whether you are a coder, tester, artist, or do bug triage: KDE neon is the easiest way to work on the latest KDE software.
Fedora may also be worth consideration, though its association with Ret Hat could end up being a limitation.
All KDE applications are well integrated, with a similar look and feel and an easy to use interface, accompanied by an outstanding graphical appearance.
Gnome and some KDE applications used to offer tear-off menus that could be positioned anywhere, similar to NeXTSTEP and its derivatives. Seemed like a neat idea that still deserves some consideration.