So, which one to choose?

This really depends on the object/class system that you want to build. A simple blessed hash will do in a lot of cases where you simply want an object plain and simple, whereas if you want a more adaptable complex system then some of the Class:: and Object:: modules will be worth checking out. Personally I rely on a simple perl data structure until I need to do anything of significant complexity, then I start to use external modules and patterns. YMMV :)
HTH

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broquaint