You can evaluate Red Hat Enterprise installing this 30 days free trial.
Created in 1994 Red Hat was the first distribution used by a whole generation of current Linux gurus. Red Hat Linux is the line dividing full command line users (our fathers or grandparents) with X windows users (We or our fathers, the second specially in Latin America).
RPM (Red Hat Packages Manager), today adopted by many distributions, was among the first packages manager lighting up in the dark times of packages compilation.
Despite in 2003 Red Hat became Red Hat Enterprise supporting corporate customers only, it is currently among the main contributors of the Linux Kernel if not the main one.