Debian is very stable. None of the Ubuntu drama with random changed to stuff like DNS resolvers each release.

I've used DietPi on several SBCs including the Raspberry Pi 2. Anecdotally, I've found the main advantage is a lot of the quality of life features that the distro offers. A file called dietpi.txt can be used to easily provision new SBCs on the first boot. The distro also has a lot of TUI utilities that can be used to connect the device to WiFi, configure settings, and install common software packages for SBCs (Nextcloud, FTP server, etc...). The creators have also adjusted a lot of the defaults such as the default SSH server (Dropbear instead of OpenSSH) and logging policy (RAM-only by default) to better match how the average hobbyist probably uses their SBC.

Much faster response time due to optimized use of I/O operations.