PHP is a lot more simpler, not to mention its huge documentation and developer following.
Although I've never learned or attempted to learn ASP, my little efforts to browse the MSDN for documentation on ASP weren't very helpful.
PHP on the other-hand has an easy to navigate documentation which covers almost every function and class in the language.
Besides, PHP is compatible with way more operating systems and databases than just Windows and MSSQL, so by learning PHP you're already opening up a lot more doors and opportunities.
In conclusion, I stand behind PHP as the better language for its simplicity, power, and cross-compatibility.