First thanx 2 all guys for valuable comments...
Please correct if wrong;
1-fuel consumption wise no such difference if we use City on CNG and 600 CC on petrol
2-shape and space wise City has more points then 660
3-@point2: 660 are quicker while running on rush road like to turning radius length etc
4-City parts easy available but not others
5-parts for both are costly means same on both ends
6-2003 City parts are older means we go to mechanic more often then with 660 cc
7-resale ...no idea about 660 cc..but city has
8-demand price for City 2003 and 2006/07 660 are almost same
any other point !!!!