I've had a few, so here's my ranking. For reference, I'm going for "mild" dirt, in that I want to be heard in the mix and a bit dirty, but not clean and not fuzz. I also want a solid low end with no loss of lows, as well as the dirt being spread out amongst the entirety of the bass tone - i.e. I don't want only highs or only lows distorted. I dislike too much high end presence in my signal, as I feel it makes my tone sound brittle, but I do want a little treble zing for clarity and definition.
1. Dunwich Volt Thrower - incredibly flexible, which is a double-edged sword. I've found that I can get pretty much any Rat tone I'd need from this, from barely there to full on fuzz. The internal trims are incredibly useful, and my only complaint is that they're internal, because every time I adjust settings, I invariably adjust those a good deal and barely touch the external controls. But maybe that's just me. Anyway, this one is my #1 as it still sounds like my tone, but dirty and still defined.
2. Blue Colander Tremond - another excellent bass Rat, and one that is also quite versatile. I find that this one does better with my 400RB-IV (the VT lives with my 700RB-II). It is also the easiest for me to dial in - literally everything at noon except tone (1:30-3:00) and volume (to taste). But plenty of settings sound amazing. It's also important to realize that the HPF functions as an HPF in that it's not a "more bass" knob, but actively reduces the mid and treble content. The HPF and tone knobs have a lot of interplay as a result.
3. Frost Giant Bass Mountain - similar tones to the Tremond, but a bit more aggressive. They complement each other well, as this one is more distorted, but the Tremond sounds a bit more natural in tone. This is also incredibly sensitive to tweaking, and little changes can yield big results.
4. Idiotbox Blower Box - I've had both standard and deluxe versions - the high end treble is too harsh for my tastes, and in the mix this just sounded like a really punchy drive, but essentially sounded clean. But hey - those could be exactly what you want! Out of the mix it's very dirty, but the dirt portion of the signal didn't really poke through the mix. I also felt this was a "lean" Rat, in that it didn't seem as girthy as the previous options. It wasn't shy on the lows (I don't think it lost lows or anything), but just didn't have the same feel to me. The Deluxe shines at 18v, and it's pretty versatile for what it is with the HPF control adding plenty of options, but I found I preferred the others for my needs. My favorite tones from this sounded like a mix of a Rat and a B3K - sort of a grittier B3K if that makes sense. Certainly a great, usable tone, but not my style.
5. Fuzzrocious Cat Tail - I had a standard version. Didn't do a lot for me on bass, though I tried to like it. I think it would have benefited from a blend, as I felt it was often either too high end or too low end focused - I couldn't get a good in-between without sacrificing something. I DID find this was excellent for my high gain needs on guitar, but that's not the discussion here!
I think those are all of my big Rats. I also tried an tiny clone a few years ago (Mosky or something like that?). It worked better on guitar, but was what got me started on Rats. Hope this helps!
(called Bass Squeak in the menus)
