M J:
You should create your theme based on Theme Parent: "classic" and Theme framework: "Velocity" (not the default Freemarker). Anything else would give you lot of griefs.
You should
not base your theme on classic. Classic is meant to be a full theme, there's no assumption of keeping it stable and extendable. Instead, build your own theme based on either _unstyled or _styled - those are the two themes that are meant for extension. _styled is the default one if you're just creating a new theme. You'll find the parent theme referenced in build.xml if you use Ant and the Plugins SDK for your theme.
An alternative to base on classic is to copy over classic's custom.css and use it as the basis for your own theme. Classic might change without notice - and you're on the safe side if you have copied a single version. Nobody will care if there's anything based on classic and breaks when classic changes.
What gives you a lot of griefs always depends on your experience: Velocity used to be the default up to Liferay 6.1 - you'll find the most samples on this language. Freemarker is where Liferay goes now. One of the reasons is errorhandling: It doesn't exist in Velocity - so if you have an error in your template, you can easily get an empty page without any content and no error message. Velocity has the lowest barrier of entry but can be unintuitive to debug. Choose your poison: Readily available sample code vs. more powerful language & debugging features.
