You should cut each branch seperate and then trim or dry. If you are going to hang dry, then trim, you should prob still seperate each branch so the plant has some room to air out and dry. If you leave a six foot plant whole, I would imagine some of the branches clumping together and just less air flow in general making mold more likely. If you are planning on trimming first, then hanging, you will prob have a hard time trimming a 6ft plant that hasn't been broken down into branches, it would just be hard and awkward. Either way will work, its just a matter of whats easiest for you