There are pretty good number of advantages to Ubuntu over CentOS (for instance).
- You get very up to date packages compared to CentOS.
- You get WAY more packages than CentOS without having to adding 3rd party sources.
- To upgrade from one version to another, you don’t have to reinstall the OS, it's just one command.
- If using virtualization, you can use "python-vm-builder" to make a special "jeos" version of Ubuntu which is cut right down for use of virtual machines. It really work fast and efficiently.
- They provide integration into Amazon's cloud services, stuff like that. Can say, they are quite up to date.
Everything sounds to be great, but if we think from a hosting point of view...
- It doesn't support cPanel.
- People think it's the desktop version so it may take a long time to convince them.
- The packages are very up to date, stick with the Ubuntu LTS (long term support) versions if you want to keep it safe.
- Although it has been out for years, CentOS has been out for a lot longer. However, being based on Debian, you can keep faith on Ubuntu LTS editions especially as being very stable. Debian has been out from last 16 years.
I hope this answers the question a bit.