php or asp.net which is best

so what you mean is those who say asp.net is good they are best in asp.net thats why they are recommending it?

Yup. Programmers will always say the tools they like are the best.

When you say you're going to "open a project" does that mean that you are going to learn programming and start building a web site?  Or does it mean you're going to hire professional programmers to do the work for you?  

If the former, you might want to look around and see what others are using.  Much of Google, all of Digg, large parts of Yahoo and nearly all of Facebook are built on PHP machines.  PHP is free and open-source.  ASP is not - it's a Microsoft product. Most of the best CMS and frameworks are built on PHP, eg: WordPress, Joomla, Drupal, Laravel, Zend, etc.

If the latter, you will probably want to engage an advertising agency or other similar consultant that has access to programming resources.  This is what I would do; it can take years to personally learn enough about application design and development to create anything you would want to deploy.  You can hire that set of knowledge and skills in an afternoon.

If you're interested in learning PHP, this article can help you get started.
https://www.experts-exchange.com/Web_Development/Web_Languages-Standards/PHP/A_11769-And-by-the-way-I-am-new-to-PHP.html

going to hire a programmer, just want to know which language will be best
i am currently discussing with some programmers, some saying php some says asp.net is best
so i am unable to decide which one to go for

Which one has more experience building sites like the one you want?  Which one can show you the best portfolio?  The choice of programming language is like the choice of cooking equipment.  No matter what's being used, Thomas Keller* will probably cook a great meal.  And I will make a mess.  Look for experience in the software developer and follow his/her advice about what technologies to use.  I would use PHP because I already know PHP, I'm well-connected in the PHP community, and I can make immediate progress with PHP.

* Keller's web site is built with PHP.

while  php will run on Apache on a Linux server

PHP can run on any machine - Windows or Linux

PHP is free and open-source.  ASP is not

They are both free, only difference is ASP comes with Windows which costs money but it's already part of the package.

Both have their advantages and disadvantages.
Both are capable of the project
PHP developers are usually cheaper than .Net developers.

According to this page http://w3techs.com/ , PHP is used about 5 times as much as ASP.NET and all of the most popular CMS packages are written in PHP.  Here on Experts Exchange, there appear to be about 10 times as many questions about ASP.NET as there are about PHP.  That suggests to me that PHP is better understood in general than ASP.NET is, especially considering how much more it is used.