I have used Debian for servers for years. If you use Ubuntu now it would be a pretty simple change for you. Any performance difference between Debian, Ubuntu, CentOS are gonna be minimal. Debian is very stable. If your goal is running a server stability is usually a high priority. I would avoid Fedora for servers( I use if as my desktop OS though). That said, if you don't have any issues with Ubuntu its fine. I default to Debian for servers but I do choose Ubuntu from time to time.