You asked this a while ago and probably have already bought something, but throwing some info out there for “posterity,” I guess…
Mixers I have known:
Edirol V4 – As @cinema.av says, this is a standard. Overall pretty intuitive. Many good features. Mirroring! Multiples! Keying! Smooth T-bar. Terrible TBC though, in my opinion. Also frustrating that there are no thru ports for the inputs, so monitoring the channels requires some splitting. Some midi possibilities here which I’ve never really taken advantage of.
Edirol V8 – Like the V4 but more inputs (though the VGA input has never worked very well for me). And then has thru for the inputs, for easy monitoring: nice! The big surprise for me on this was how much I love – and use – the added feedback effect. Super dreamy. That all being said, probably not worth the extra cost over the V4 (though if you watch Ebay long enough, good deals do come along; I picked up mine for not too much more than a V4).
Videonics MX-1 – Generally overpriced for what you get, in my opinion. Too much menu diving, not enough knobs. More of a program-in-an-effect-and-then-run-it machine than something made for on-the-fly experimentation. Requires a monitor for its menu at basically all times. (Haven’t used a mx3000 but it does look to have a ~somewhat~ greater compliment of front-panel controls.) This thing does have some nice cheeseball effects though. But basically only pull it out when I need its very flexible (if also kinda terrible quality) chroma keying.
Panasonic MX-12 – Very limited, but kind of magical. Its luma key only keys to a background color (it was meant for titling), but it has very fine control over the levels and so has a look all its own. (I don’t have one, but if you get the MX-10 instead, you can apparently mod it to do a full luma key of one channel into another.) Some nice, wide color shifting, as well as some ho hum but usable digital effects (no mirror or multiples though). Its TBC clocks from one input, so you need at least one stable signal going into it. But, if you have at least one that is stable, I’ve found the other one can be quite glitchy and it will generally handle it like a champ (without diminishing the effect too much either). Terrible T-bar.
JVC JX-SV55 – Okay, this one isn’t really a “mixer” (you can only mix with solid colors, not between channels). It is a two-channel “switcher,” at best, but really a “processor.” Wouldn’t even mention it except for the fact that it can do one thing exceptionally well: super wide color shifts, controlled by a joystick. So useful for feedback. I think I picked it up off eBay for ~$25-35 shipped. It’s not going to do everything for you (or much at all), but if you find one for a good price, it’s a no-brainer, I think.
…In my fixed set-up, I use the MX-12 together with one of the Edirols (currently the V4 because I haven’t patched the V-8 in yet), as neither does everything.