I have been designing websites for a while now, but there is one thing that I have never been quite sure of when using PHP and HTML. Is it better to have the whole document
Simple:
More PHP - close HTML in PHP. When you generate HTML code in PHP, when you are doing something like a class, so it is better to make it in echo.
Less PHP - close PHP in HTML. This is stuff like just putting vars into fields of HTML stuff, like forms... And such.