My personal Favourite : The Windows XP x64 ….. it is very secure and old look and feel of xp makes it best of the best……
I would rate vista x64 ultimate edition 2nd to it…. The looks of vista are fancy perhaps more of waste of resources i’d say…. but ya if u really want the vista look go for 64 bit ultimate edition only…..
The major advantage of 64 bit windows OS is not only its high speed but of the fact you are safe from malicious device drivers…. The drivers need to be signed then only they are installed….
I’d like to add that i m not going into details of vista’s false security claim coz it is a universal fact now….