[GG-Xtreme]

Since you didn't limit a mobile platform, I'd have to choose between an UMPC running XP/Vista, or my PSP, which runs XMB, uCLinux, MS-DOS, Windows 3.1.1, Windows 95, Windows 98, MacOS 7.5.5, MacOS 8.1, NervOS, IRShell, project4, NES, SNES, N64, GB, GBC, GBA, PSOne, and Sega DreamCast (last one is new and very slow, everything else is either full speed or very useable).

[jaco_don]

Symbian UIQ ... are life and best for Mobile device ...Windows is cool ... but haven't used it

[allinone]

symbian is best.reason is it have largest softwares available for it, games are there many applications are there which are not available for other os, its the most widely used os........