What are the 6 most powerful weapons (or weapon combos) in the game?

[Crenshinibon]

The staffs are good, yes, but the knockback, it's just a fancy feature that doesn't really help unless yo want to go ranged all of a sudden. Also, if you can go invisible, you don't really need that ring. The only reason I'd use it is to make a Blade mobile while using Defensive Stance.

[Celacena]

I agree that with targeted attacks, being invisible is enough, but there are some area-effect spells that can immobilise, slow or otherwise impede the PC.

I just like the security of knowing that I'm almost untouchable when on the run.

I often use the shield of harmony to prevent disabling attacks - it is a shame that the staff and the shield cannot be used at the same time. I think there are other items with mind-protecting features, but I cannot recall them all. when not doing the run and return, my thief uses that shield and a sword when backstabbing.

[Crenshinibon]

By the time you get UAI, the two AOE spells you should be afraid of (Hold Person and Web) are nothing. Spell Trap should take care of the rest. When backstabbing I usually go for Staff of the Ram +6 but sometimes use Sword of the Mask +5 or Dagger of the Star +5.