Is the first or second method more secure, or does it not matter? Plus, which method would "execute" faster or get interpreted faster by the PHP parser?
As Crash said, no, both are just fine. With regards to performance: if there were a difference, it would be negligible (near zero).
However, I would argue that the first method is more readable
than the second. Why bother encapsulating HTML inside an echo statement when all you're doing is outputting HTML to begin with? Just print the HTML and don't worry about echo - only echo if you need to do something like:
<p>I am doing fine, but when I checked my weight this morning, I weighed <?php echo $weight; ?> lbs. </p>
Strive for readability, performance is negligible.