I A-B'd the MMGs and 2Cis in my living room about 9 months ago and, while they both sounded nice, I don't think there was any question which had more detail and realism. The MMGs are, as previously mentioned, an inexpensive way to get into their product line, but in no way come close to their better models. The Vandersteens disappear and you just hear the music, not the speakers playing music. However there are always other considerations, and some may opt for the modern, flat panel look of the MMGs over the very clean but plain looking Vandersteens.
I also, surprisingly, found the most noticable difference to be in the upper ranges. The Vandersteen theory of putting the money into the speakers instead of the cabinets really became apparent. The Maggies rolled off and did not convey the details in the music in the high end. They were auditioned using both tube and solid state amplification, a Bryston 4B-ST and a pair of Quicksilver 60 watt monos.
Another thing to consider is that the MMGs are about $550 new, while the comparible Vandersteen model, the 2Ce, is close to $1500. I know you mentioned used, which places them in the same ballpark price, but I have to tell you you'll be getting much more for your money, sound-wise, with the 2Cis. Now, if you were compareing 1.6s and 2Cis, it might be different...
Whatever way you choose to go, you'll have fun. - Jim