Option 2 is faster. you should always single quotes whenever possible since PHP does not need to look for variable expansion. what i do usually is use the "." concatenation operator with variables.
this will execute faster:
echo 'this string has a ' . $variable . ' in the middle';
this would be (slightly) slower:
echo "this string has a $variable in the middle";
also since most people use double quotes in HTML using single quotes in PHP to echo it requires less escape characters