I work with both!
I think that it really depends on what you are going to be doing with your site.
ASP hosting is a little more expensive than PHP hosting. ASP is a little slower than PHP.
ASP is simpler than PHP. That makes it a little easier to learn, but once you get into it, doing anything a little more complicated is much easier in PHP. Being a language written by the people that actually use it, there are so many useful little functions, that ASP just doesn't have.
Anything more complicated in ASP requires installing external components (DLL's)! Which a lot of hosts dont like to do.
My recomendation, is if you are setting up a new small site., going for cheap hosting, and dont know either ASP or PHP, then go for PHP. The learning curve is not all that much steeper, anyway you can get all the help you need here!