Despite the facts of needs (you can still use ASP on Linux, but not as well), Linux is generally more stable and easier maintain, and often times more secure.
Open source community is more Unix oriented, which makes it more useful for Hosting companies, from financial point of view. On the other hand, if you have a good base of Windows clients....
I would suggest LINUX. As it’s much much cheaper than Windows. If you ask me what if I do not know how to manage it..? Then I would say have Cpanel on it.I think Cpanel on Linux sever makes it best of all.
Also Linux have tremendous stability with flexibility and above all its VIRUS FREE
This topic is old and I think that although there wasn't any obvious answer (which is obvious as it is a "per opinion" topic), but I think the thread can be closed.