Presently I'm using almost all OS based mobiles(except maemo),In my personal opinion,my favourites are:
1.iPhone (MacOs)
2.Windows Mobile
3.Symbian
4.Blackberry
5.Android &
6.Palm OS
*i483.photobucket.com/albums/rr199/dhan_shh/DSC01712rJPG.jpg
Choice and taste may vary from person to person,but overall iPhone suits most people.
Bada OS and Maemo need further evaluation.