I've owned both types, but they were sufficiently different that any sonic comparision couldn't simply be boiled down to MM vs. MC. From what I understand, the main theoretical advantage of MC design is lower moving mass, something that's easy enough to comprehend. The disadvantage, as stated above, is usually lower output, requiring greater phono stage gain which can impair S/N. From what I've heard (not nearly as much as some, I'll admit), I frankly think that if you correctly load an MC for smooth response and tight focus, rather than letting it run away unloaded to get "air" and bigger-than-life images, then the differences between it and an equivalent-quality MM can be fairly academic if each is mated to an optimally-matched phonostage. But if forced to generalize, I would say that a good MC can win on transient speed and harmonic detail, while a good MM can win on dynamic punch and tonal density. It might be interesting to hear the newer Grado MI carts (they are moving irons, right - not moving magnets?) with the ultra-low outputs, which presumably would have much lower DC resistance (that is, fewer coil turns - like an MC) than typical higher-output models. To me, as a guitar player, the whole question is roughly analogous to the single-coil (Fender) vs. double-coil (Gibson - known as "humbuckers") electric guitar pickup choice. A lot (but not all) of the differences in sound have to do with the ways lower (single-coil) and higher (double-coil) output voltages will drive a guitar amplifier's input stage, and whether the frequency response is more extended in the upper ranges (single-coil), or emphasizes the mid to lower ranges (double-coil).