I've always been a fan of Debian-based distos over Red Hat based, so I've been quite happy to see the shift from Red Hat to Ubuntu in my career as a Linux admin(the shift away from Red Hat is stronger on the web side, but its happening across many server types).
On Debian vs Ubuntu, I'm actually preferring Ubuntu these days because the LTS release cycle is just much more predictable(but don't do prod servers until LTS.1) and it's easy to get a life cycle in place. It's also much easier to get third part software prepackaged for Ubuntu in versions that may not have shipped with your LTS version. They may work for Debian too, but I've had more luck getting Debian only versions working on Ubuntu than Ubuntu only versions on Debian. Probably because the Debian-only versions are more likely to be thoughtful of Debian derivatives.
I recently took advantage of a major clean-up re-install to switch a couple of my VPS servers from Debian to running Ubuntu server. I haven't noticed any difference at all as regards speed or stability and, with Ubuntu, it's just so much easier getting up-to-date versions of software.
I think Debian sometimes errs a bit too much on the side of caution, as regards not going anywhere near the "cutting edge".
On Debian vs Ubuntu, I'm actually preferring Ubuntu these days because the LTS release cycle is just much more predictable(but don't do prod servers until LTS.1) and it's easy to get a life cycle in place. It's also much easier to get third part software prepackaged for Ubuntu in versions that may not have shipped with your LTS version. They may work for Debian too, but I've had more luck getting Debian only versions working on Ubuntu than Ubuntu only versions on Debian. Probably because the Debian-only versions are more likely to be thoughtful of Debian derivatives.