Linux is a popular choice among operating systems. Deciding on Linux is however not enough. You have to pick a distribution and the list of choices can be overwhelming. Others have tackled the question and here are some answers:
- DistroWatch.com has an excellent list of Top Ten Distributions
- linux.com published a list of The Top 7 Best Linux Distributions For You by Brian Proffitt
- techradar.com featured a list of 10 best Linux distros by Graham Morrison
- reallylinux.com published a well structured analysis on Choosing The Right Linux Distribution by Jethro Carr
An answer depends on the need. For me the primary need is for servers running SaaS applications and databases. In such scenario solid features, stability, reliability and longer term support are key requirements. Availability of professional support may be desirable as well. Distribution which consistently comes to the top of the list for such needs is CentOS/Red Hat Enterprise Linux. Ubuntu, with its Long Term Support version, is also a common choice.