I recently found what I believe is that fastest BUD switch, as it requires no torches nor repeaters. Credits go to SethBling for the original version, I only made a few tweaks to it. It requires 13w10a or higher.

It gives out a one tick pulse, and resets extremely fast. It uses a new mechanic with the upside down half-slabs where if the redstone is pointing to a redstone usable block (In this case, a piston) it will power it. This was not so before 13W10a.