With Joomla the best PHP choice so far has been suPHP. All the other PHP choices have led to unexplained installation/configuration/usage problems that keep cropping up and hitting you in the back of your head when you are least looking.
Here's hoping that Apache2 with PHP-FPM can replace suPHP. The jury is still out on that one and I personally would not use PHP-FPM with (Joomla) Virtuemart web-shop yet (unless you are looking for trouble.) We will see when we get more experience with it's problems. No PHP is perfect.