That depends on your skill. A general observation I have made is that Linux hosting plans are cheaper than Windows Hosting plans.

Stick with what you know. If you're comfortable with ASP .Net, use that, if you're comfortable with PHP, use that. If you don't know either, then decide which one would you prefer to learn?
Ok... currently, i don't have knowledge in either of them... But some of my frnds have... And I am going to learn them... So, according to my knowledge(dont have too much ), if I want to use Linux hosting which will be cheaper, I have to use PHP with MySQL. If using Windows hosting, I have to use ASP.Net and SQL Server....
Is that right..?