Personally I enjoy Agni & Rudra, Lucifer, Red Queen, and Yamato.
Agni & Rudra is plain fun to use! Dante could be extremely agressive with those blades in DMC3. Besides Nevan, Lucifer is the most unique weapon I have seen - I still haven't been able to play with it a bunch though. Red Queen's Exceed system is excellent once you get used to it - I'll have up a little something about this in a few days. From Vergil's use of it, Yamato's speed and reach was the main aspect that I enjoyed about that particular weapon. I liked its overall power also depending on the attack used - Judgement Cut, Aerial Rave.