PHP is more widely used but ASP.NET seems like the pro thing. I would say go with php because there are more resources avaliable to you on the web.

Not sure that is true, ASP.NET is much more in demand than PHP in terms of what companies are looking for, Java is also very popular. PHP seems to be the language that kids use and then they try and apply for a job and realise they should have spent their summer holiday learning c++ or java.