i've never used one, but from what i've read on here it seems a lot of people on this forum really like the G Major with the Mark IV's serial loop, whereas it may be a little trickier to use with the parallel loop on rectifiers.. (someone jump in if i'm wrong)
i know a couple people who have recently picked up the Boss ME-50 as an affordable, floor-based, all-in-one multifx unit, without all the amp modeling mumbo-jumbo that's in a lot of multifx units like the Boss GTs and PODs and the like.. they're all way stoked on it.. fair price, classic Boss effects, pretty sturdy contruction, and not overly complicated to set up