which is been the best oprating system?

Most used is windows

but now days mac, android and linux are getting more crowd

It depends on the use.

For general desktops running commercial programs and games, Windows 7 (or XP on an older machines) is probably the best.

For servers, storage machines, VoIP systems (Asterisk servers etc) and anything that requires ultimate stability and reliability, an Enterprise-grade Linux version (such as Centos or Scientific) is the best without any doubt.

For tablets, both Apple IOS (originally based on Unix) and Android (a form of Linux so also a Unix-type system) both have advantages.

Linux is OK for some types of desktop systems. The downside is not Linux itself, but that so many applications are only available for Windows systems.

The Apple Mac desktop operating system has similar advantages with stability but disadvantages with software availability.

[Electronics designer & programmer for 30+ years]

So far XP and Win7 are the only really good operating systems, Vista and Win8 both suck Batman balls.

XP Coz some prog like c, c++, java doesn't working in windows 7.

For what? Desktop or mobile? More specific.