There's two things I think every bitcrusher should have: 1. mix / blend control, 2. expression control input and / or an LFO.
These features just make the bitcrusher effect so much more useful and versatile because with the mix / blend you can tweak it from full out madness to a light harmonic shimmer on top (this can be really beautiful) and the expression / LFO makes it way more dynamic.
Most bitcrushers have a maximum resolution of 8 bit which in my experience makes for an effect that goes over the top of what you play instead of really integrating with your signal.
I currently have a Hexe Electronics Bitcrusher III and a Iron Ether FrantaBit and they're both great but quite different beasts I must say.
The FrantaBit has a range from 24 bit to 1 bit so when you sweep the bit depth it sounds much more extreme than most other bitcrushers.
I mainly use the Frantabit for harsh gated synth effects (minimum bit depth and maximum mix) and complete destroying of a loop or something I play (bring down the sample rate with lower bit depth) down to just some crazy watery warbles or screaming noise.
It's also possible to dial in some absurd gated synth fuzz tremolo like sounds that vary in speed with the notes you play, freaky shit!
I contacted Taylor a few times to ask some things about the pedals and he responded very quickly so in my experience the costumer service is very good.
Good thing about the Bitcrusher III is it has a range from 12 bit to 1 bit which is kind of a sweet spot I think.
It has also got the Telephone filter which is very useful for dialing in computer sounds but it can also help taming down the treble of another effect (you can use the Telephone filter on the Bitcrusher III without the Crush or Downsample) which makes it quite a versatile pedal (I use it to tame down the highs of the FrantaBit sometimes).
The Downsample on the Bitcrusher sounds incredibly sweet and is great for laying harmonic shimmers on top of your signal, which I use it for mostly.
Another cool feature I end up using quite a bit is the LFO, it's just so easy to use because the LFO sweeps the downsample parameter for you so you don't have to use an expression pedal all the time, it's really great.
Customer service is also really great because Piotr is helping me by programming a different bitcrushing algorithm into my pedal (the current one is just a bit too sensitive with my setup and gives me some noisy artifacts I don't really like) and also tweaking the depth of the LFO to go a bit deeper on high downsample settings (faster speed) so I can get more of these freaky yayaya sounds and that kind of stuff.
By the way, for the real tweakers Piotr released the new Bitcrusher III Studio Edition:
http://www.youtube.com/watch?v=07ZgzIhDJpMQuite a bit of money but that thing is a true beast with the four crush modes, seperate LFO's for Crush, Downsample and Telephone parameters and MIDI control.
I also tested the Geiger Counter but for me it was too much, it's really not useful for live applications in my opinion, and offcourse it lacks a mix / blend control which I think, especially in the case of the Geiger Counter with the high gain preamp and 8 bit max resolution, is a fail.
I never tested the Biscuit but that one would have definitely been on my list if I wasn't particularly looking for a bitcrusher in a guitar pedal format.
It seems quite expensive but the filter is supposed to be really great, add in the step sequencer and the fact that you can also use it as a synth that makes it great value considering these options aren't too overwhelming (could be for me).
