Arduino communicating back and forth with PHP server I am researching to find the best method to work with in order to control the arduino from a web interface (hosted on a web server using PHP) and also sending data from arduino to webserver and save to mySql.

2 methods which I have found that a lot use are save the data to a text file or in the url.

Which is the best or are there any better methods?
I would suggest your best bet would be to pass messages back and forth via JSON, via Get/Post http request.

So to send data, you send a POST request (to the PHP server) with your data in JSON in the content.  To get instructions, you send a GET request to the PHP server and get a contents field with JSON in it.