This argument is won by PHP purly and simply because ASP is old news.
If the argument was ASP.NET vs PHP then thats a tricky one.
When coming to pick which one to learn then its comes down to for what reason are you wanting to learn for? Is it for a hobby? then I'd definately pick PHP. Or is it because you want to work for a big firm that uses microsoft as it main OS? Then ASP.NET would be more useful.
My personal choice still falls with PHP on the grounds that any web technical challenge I've encounted I can solve with PHP.