I'm gonna have to go with Gunvolt here. His flashfield inherently stops any attack Ichigo would release minus a getsuga, as all of his other attacks are close range. Not only that, but the profile notes that it's a commonly used ability. And, by nature of it being a forcefield, it would inherently provide some protection against Ichigo's getsuga. Literally this one technique covers the entirety of Ichigo's arsenal, and he has more than that. Ichigo would have difficulty getting past his regen, as well as the somewhat randomly spawning streaks of electricity being fired from his gun.
It's true that his chains and summoned swords may not do much as Ichigo has similar experience from fighting Byakuya, but any attempt to block them as he often was forced to do against Byakuya, would result in his being shocked with electricity, causing him injury and slightly slowing him down, with a chance to even paralyze him.
Psuedo-invulnerability makes this even more unfair, as Ichigo first has to get past Volt's most commonly used attack by using the one thing in his arsenal that can potentially get through it. And even if he does manage to successfully close the distance, he won't even be able to harm Volt, and that would likely leave him wide open to be paralyzed by the latter's electricity, before successfully being struck down by a blade or gunshot to the face, or even being immobilized by chains before the paralyzation wears off. I think gunvolt takes this mid-dif, simply by virtue of him having far more versatily options, as well as his most used option essentially countering Ichigo's entire moveset at this point.