As answer one has stated this is a big topic that is really more a matter of preference. If you want to utilize RAID you are better off with debian over sunse redhat or mandrake. Debian supports more RAID hardware but lacks the lustre of redhat and mandrake ease of use. Sunse tends to be more networking ready from a user profile standpoint but again has less userfriendly interface. Mandrake was originally an offshoot of Redhat that supported a much improved installation structure but quickly became a system in it's own right. And Redhat is parallels Mandrake with similar installation and user GUI.
To bring you up to speed you can find concise information about linux at my site at
http://alltechdevelopment.netfirms.com/index.htm and follow to the linux topics centre-left of page for the topical links.
regards
rick