[Skunkworks] LINUX PROXY/FIREWALL AS AN ALTERNATIVE TO WINDOWS

Hello All I am currently using a microsoft firewall for a corporate Lan.however of late this firewall misbehaves and brings major downtimes. Am talking about Microsoft TMG Am looking at something that can do 1) Proxy Services eg browsing,Reverse proxy etc 2) SMTP 3) Web Publishing 4) Firewall I have searched and i have gotten the following alternatives 1) ClearOS 2) Ipcop 3) Endian 4) Pfsense I may have left others My questions are 1)Which would you advise to be good in terms of Functionality 2) Can they be configured in a cluster mode 3) support ,how is it? I would really appreciate any feedback Regards Cynthia