Which do you use and why?

Also, are all of these valid php statements? Is one method better than the other speed wise?

PHP Code:
echo '<div align="center">Welcome. <a href="/">Click here to return home</a></div>';
echo 
"<div align=\"center\">Welcome. <a href=\"/\">Click here to return home</a></div>";
print 
'<div align="center">Welcome. <a href="/">Click here to return home</a></div>';
print 
"<div align=\"center\">Welcome. <a href=\"/\">Click here to return home</a></div>"