⟩ Tell me which is best os ios or windowsphone or android or meego?
Meego doesn't stand a chance because of it's limited availability, and the fact that it's just overly simplistic. If you want simplicity, go for Windows Phone or iOS. It doesn't even deserve to be on the list.
Windows Phone is my second choice out of all the phone operating systems. Its's very simple and elegant (even more than iOS), and is extremely stable. You will also be able to link it with Windows 8 when it comes out, and there's a possibility you could eventually run the full Windows 8 on it if it's fast enough. The only downside is that the app store is a bit small, and only has the basics currently.