Another thing to point out is that there really is no difference from the second one and the third one other than single quotes and double quotes. I prefer single quotes because double quotes looks really messy. Also, you generally don't really even need double quotes for anything. If you want to use variables in a string that has a string already, you just concate it like so.
$string = 'My first string ' . $var;
And it would achieve exactly what this does.
$string = "My first string $var";
And if you want to use a single quotation in a string like
I haven't really done that, you can simply escape that single quote nested in other single quotes. IMO, double quotes are abused so much in
PHP that most people place double quotes in the wrong way possible.