Which OS do u think is more stable?
Linux or Windows

Linux is free and windows has to be paid .. so in this respect windows can be said stable but in the sense if you want more features in low cost then linux server is the good option

Its depends on the management team deploying the server and O/S so the answer is really neither. Also keep in mind there are several versions of windows and a dozen common versions of Linux out there making servers work, so in that sense this is a really loaded question.

The most stable O/S in linux we use is Centos 4 or 5. That's our personal choice.

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As for me, I prefer Linux, because it is easy-to-operate system.