$_POST vs. $_SERVER['REQUEST_METHOD'] == 'POST'

Well, they don't do the same thing, really.

$_SERVER['REQUEST_METHOD'] contains the request method (surprise).

$_POST contains any post data.

It's possible for a POST request to contain no POST data.

I check the request method — I actually never thought about testing the $_POST array. I check the required post fields, though. So an empty post request would give the user a lot of error messages - which makes sense to me.

if ($_SERVER['REQUEST_METHOD'] == 'POST') is the correct way, you can send a post request without any post data.

I used to check $_POST until I got into a trouble with larger POST data and uploaded files. There are configuration directives post_max_size and upload_max_filesize - if any of them is exceeded, $_POST array is not populated.

So the "safe way" is to check $_SERVER['REQUEST_METHOD']. You still have to use isset() on every $_POST variable though, and it does not matter, whether you check or don't check $_SERVER['REQUEST_METHOD'].