It all depends on your preferences, but Apache+FastCGI Process Manager (a.k.a. PHP-FPM) or Nginx+PHP-FPM is usually the best way to go.
As for choosing between Apache or Nginx, you will usually not find any signifficant difference. In Bitnami we offer most of our Bitnami stacks with Apache, as it is more easy to customize and extend. You can find an example here: https://bitnami.com/stack/drupal
If you want to use Nginx instead, check this link: https://bitnami.com/stack/nginx Note that you will need to install Drupal on top of it.
You can read more about PHP-FPM here, if you haven't enabled it yet in your Bitnami stack: https://docs.bitnami.com/virtual-machine/components/php-fpm/
Let us know if you have any questions.