Is it better to echo <<<_END all my html and php code

I use notepad++ as my editor. I like using notepad++ because it is simple and light weight.

notepad++ no longer highlights matching html tags within a php code block. I google for a solution. People at other sites have written about the same problem. It is being recommended that the proper way of coding is to embed the php code within <?php tags ?> at multiple locations throughout the html code. This makes it easier to read the code because the code has color.

I use to do it this way but changed it to putting all my html and php within <?php tags ?> and using echo <<<_END html and php _END; This made the code all one color which is more difficult to read but it was my understanding that the code is more efficient and renders faster using <<<_END.

Is my understanding correct?
If my site had millions of visitors like yahoo or facebook, what should I do? Thanks.