PHP vs ASP
It really depends on largely what you are trying to do, and the language you are most comfortable with. My teachers always told me that there are 50 ways to skin a cat (no disrespect to you animal lovers, b/c I mean none), its the same with coding though.
1. What type of server are you hosting the code on?
2. How large do you anticipate this project to be?
3. What is the cost budgeted to maintain this content?
4. Will there be a team working on the project, if so how large, and what code are most members of the team most comfortable with?
etc.