Well it's better than the Bount arc at least, and probabally the best filler arc in Bleach though that's not saying much....
If the Zampakuto filler arc would have ended as strongly as it started instead of fizzling out I would have said that one was the best but it totally fell apart at the end after Muramasa was out of the picture.
Should have ended it after Muramasa bit the dust, instead it lingered on like a sick old cat.
The "Rouge Beast Sword Arc" after the Zanpakto arc should have been three episodes at most, not 1/2 a freekign season.