Check out Ghostland Observatory if you haven't already. Can't wait to see them firsthand.
As far as the thread, I am going to have to agree with some others before me who said things along the lines of "Comparison not possible".
As far as live shows go, Mars Volta is , especially in an outdoor festival setting. Lead singer becomes possessed!!!
MGMT is more like chill out type music to me. I love listening to their shit for the burn down, aka . I heard they suck ballsacks live tho...