Choose Beautifly. Beautifly has Stun Spore and an average Special Attack. However, this is nothing compared to all the other low stats and x4 Rock weakness. Dustox is even worse though. Being slow, and having Special Defense as the best stat (not even being able to survive a special attack still mind you) also not being able to do any damage. I suggest not adding either to your team. If you want a Neverused Bug type, choose Venomoth. If you just want a good Bug type, go with Scizor, Forretress, Ninjask, Yanmega, or Heracross