I have both the K1m and FB-01 and can safely say that the FB is way less noisy. It's one of my fave synths, small, powerful and very flexible. However, contrary to the K1m you will need an editor to access all the deeper FM synthesis functions as there's only a limited set of options available via the frontend. I use YSEDITOR (FB-01 version) on Atari ST, also works with Steem (Atari ST emu). However, there are other good editors available for Win and Mac as well.
FM synthesis is my fave form of synthesis ever. It's not as easy to get into as classic subtractive analog stuff but even a small 4op FM synth like the FB can do things you won't be able to do on most standard analog monos or polys.
In short, ANY electronic musician should own a FB!
About the Volcas, the Beats is my fave of the lot so far and I also love the Keys. I had my probs with it at first but if you've come to grips with the filter and resonance (it has a dramatically different filter than, say, the Monotribe or Monotrons), this thing really shines... ...and man, does the ring mod poly mode sound cool!
The Bass is excellent and gives you tons of features and a good sound for the money. The thing is, I already have a good selection of bass/mono synths (original 202, BassStation, MFB Nanozwerg, etc.) so I use the Bass for other stuff, mostly polyrhythmic or fx-y sounds.
Since some people keep asking me this question: The Bass is not the best 303 emu I've used so far, I'd even rate the Monotribe superior in this regard. Still, you can coax some nice lysergic sounds out of it and it has enough bottom end to make it a great little bass box.
Another word on the K1m, I LOVE this thing to death, it's absolutely perfect for creating all sorts of weird textures and has some interesting synthesis features you won't find on other machines, like the envelope delay which can be used to create some wavetable-ish stuff. I'll never sell mine.
