I use both Debian and Ubuntu, and they both perform well, but here are some reasons to choose Debian over Ubuntu
Read them here
3) If youre using a Special Computer Architecture
Debian now runs on eleven different computer architectures, and these ports are still in active development, so youre sure yoll get something good. x86-32, x86-64, PowerPC, SPARC, DEC Alpha, ARM, MIPS, HPPA, S390, IA-64 are currently supported architectures.