G1N; this is the cheapest one (although I think it came out after the G2 if that makes any difference). you can get them from various places around the web for only $60 shipped.
I bought it mainly for the amp sim and speaker sim for recording purposes. I previously had a line 6 pod that I used for this purpose, and would use various pedals of mine for drive/distortion and anything else. this thing excels at that task, but also I've never really messed around with a multi-effects unit such as this and I have to say it's incredibly useful. I'm not sure why more people don't use these. it's very high quality digital audio. 24 bit, 96kHz. that's more than twice the sample rate of CD quality audio, ensuring your signal isn't going to be harmfully mangled in any way. I was impressed with the inclusion of more unusual effects such as ring modulator, slow gear like effect, pitch shifter/harmonist, and whammy like effect (which can be controlled with an expression pedal) that all perform very well.
the only apparent drawback is that you don't have control over all the parameters for the effects (the higher up models do however). but assuming you already rely on stand-alone pedals for your sound then this can easily function as just an extra bag of tricks.
every processing stage can be turned on or off, letting you save presets for individual effects or other processing. all in all a very inexpensive way to bag a dozen or so useful effects/processors.
