I use a turbo tuner. I chose it for its speed, accuracy, simplicity and that it's true bypass (and it doesn't drain the battery if you are plugged in and not using it!). I used to have a Korg Pitchblack which I also liked for similar reasons. The only upside the TT really has for me is that it doesn't take up a spot on my PP2+
Timing has a lot to do with the outcome of a rain dance.
I used TU-2's for a long time and have tried quite a few different ones, but I've never used anything close to Sonic Research's ST-200. It's far more accurate than anything else out there that I've ever come across:
I use the Turbo Tuner. It's accurate, has a fast response and is true bypass which I wanted. Also, it has a small footprint. It pretty much wins on all fronts, in my opinion.
amps: Morgan AC20 Deluxe 1x12, brown Princeton, Silvertone 1482, Ampeg Gemini II, '63 Vox AC30, Harmony h430, Dr. Z Mini Z combo, Alamo Montclair... Etc...