I personally like PHP better than ASP. As far as the advantages of each. The main advantage PHP has over ASP is that it is open-source and is Usually used in the LAMP(Linux, Apache, MYSQL, PHP) configuration. There are companies like Chilisoft that have 'nix versions of ASP but it is not opensource. As far as the other advantages, here are a some articles on the battle:
http://php.weblogs.com/php_vs_asp
http://www.oreilly.com/ask_tim/asp_php.html
http://cyberiot.com/php_vs_asp.htm
http://www8.ewebcity.com/wfeng/home.asp