TurboTuner and Pitchblack are both nice. Pitchblack+ also serves as an A/B switch.
However, both of them have one "feature" which I find to be a drawback - they always mute while tuning. The up side is that they don't use power while not tuning, and they are both true bypass. But I really wish they had an option to keep the tuner active and pass the signal through at the same time. I get around this at the moment by using the Pitchblack+ as my A/B switch and "muted" tuner, while feeding the TurboTuner from the tuner out on my amp (so it's always on).
I believe the Peterson pedal tuners (StroboStomp 2 / Stomp Classic) can be configured as either true bypass OR constant tuning (with signal passed through). I probably would have just gone with a Peterson if they had a model with the A/B switch built in like the Pitchblack+. Oh, and I think the Peterson's have better support for Buzz Feiten tuning - which would be more of an issue if my MTD z6 wasn't fretless...
Petersons have had a lot of positive feedback on TB, although there have been some durability issues with the displays on older models. TurboTuner and PitchBlack have also been well received and deservedly so. IMHO, any of these three would be a substantial improvement over a non-strobe tuner.