I've developed web apps in java, c#.net and PHP. The latter has always proved to be a more productive platform that produced the most maintainable code and faster results.

Choose PHP if:

* You want to develop a web app that runs anywhere (especially if you don't own your own server)

* You don't want to write everything yourself (the PHP community is huge and they tend to share code and solutions more than other)

* You want to be able to find documentation on everything with samples of how to do things. (php.net just plain rocks)

Use java or asp.net if :

* You need performance

* You need less talented developers in your team produces better code (compiled statically typed languages tend to prohibit you from making stupid mistakes)

* You prefer to use official libraries rather than 3rd party open source ones.

* You absolutely need an IDE. PHP as all dynamically typed languages are harder to debug and/or monitor.

Very powerful language but not for large business projects.

Some libs (for instance handling Excel) are poor

it is my first learn language

although i'm not familliar with this scripting language. but it's very powerful in web development. So many php web hosting services on the web compared to java web hosting. it greatly accelerates php development and its popularity.

One thing to tell about PHP, You can built what you imagine with PHP. Its very user friendly and its library is very rich and getting richer day by day. I think the Array and Date library of PHP is best of any language. I also love the CURL library, too. Hope you will enjoy this too.