There are two major scripting languages: php which is free and open-source and asp.net which is proprietary. They act in similar ways and can be used to develop web apps alike.
However i prefer php because of its numerous frameworks which give you alternatives. Also resources on php are readily availabe. The major advantage asp.net has is the fact that it is object oriented by default which makes it difficult to write codes that are not object oriented.
It all depends on which language you feel most comfortable with.

source: http://ericadewumi.com