It depends on the job. Learn them both. Actually, learn lots of languages. Learn how to program well. I've had lots of arguments with non-programmers about how a programmer should stick to just one language and learn it really well.
Actually, I haven't. Once someone pulls that card, I add an ignore flag and let it go. It's not worth trying to educate someone like that. They have their opinion, and nothing I can say will change their minds.
But. To someone who wants to learn how to program (a few years of javascript is a good start, grasshopper). Plan on learning at least 1 new language a year. Make that one of your main goals in life. I see this bit of advice over and over on the 'net. There's a reason for it: it's excellent advice, and people don't listen.
You may wind up learning some obscure language that you never get a chance to use in the Real World. Doesn't matter. That language will expand the way you think about things and approach problems. (Hey, I could do this if I were writing the program in ThaiKungFu. Why don't I add a class that does this and saves me a lot of trouble?)
Here again, I'm wandering off-topic. ASP vs PHP. Depends on what you want to do.
If you're wanting to create websites for yourself, on relatively low-budget hosts, plan on PHP. You (as individual) will probably get more mileage out of it.
If you want to get a job with a company that will pay you insane amounts of money for very little real work, learn ASP.
If you want to develop a serious web app that handles some really hard-core problems, look into plone. There's probably something similar based on perl.
