Choosing a the best Linux distribution in the beginning is not an easy task. If you’re looking for a list of the best linux distribution for web server here is a review of the top rated linux distro for web server like apache.
If you’re looking for stability you want to keep to stay on Debian derivate like Ubuntu for the capability of upgrading easily with apt-get update and apt-get upgrade command without any problem. Absolutely to avoid things like Gentoo that can lead you to an unstable or problematic system if you’re not familiar with the compilation of programs.
You want also avoid Fedora or Red Hat expecially if you have are doing edge software development in Ruby.
Instead if you’re looking for long term support and you have the chances to pay for those services then your best options is to choose between Red Hat and Ubuntu.