Ok, all of these irons are considered "Blade Style" irons. So they are very similar in almost every way. The mp33 is a muscle back blade style iron. This model is forged, as almost all Mizuno irons. This means that the alloy was rendered through a different process than casting. Forging makes the metal softer for better feel. This club is non-forgiving and is for low to no handicap players that are superb ball strikers. The mp32 is what is referred to as "Cut-Muscle" this is a concept that Mizuno is the flagship of. All it really means is that it is the mp33 with a slightly bigger sweet spot because the weight to the clubhead is distibuted barely more to the outside. These forged clubs are exceptional in every way. The mp-60 is the least workable and most forgiving of the three. Although this club is more workable than that of probably almost any other companies muscle back designs. These clubs are more forgiving because they are far more perimeter weighted than the other two.These clubs are also forged. The similarities between the three make them hard to distinguish what makes them different.
Here's an easy way to keep track
MP33 - most workable, least forgiving
MP32 - extremely workable, more forgiving than MP33
MP60 - least workable, most forgiving
By workable I mean the ability to play shots with side spin, ie fade, cut, draw etc.
But these clubs are the best money can buy in my humble opinion. If I had a grand to blow on irons I would play them in a second and you can bet your ass.
Here is a link to a website that goes into a little more detail than what I just wrote here:
http://www.iwantgolf.com/mizuno-sets-irons.html
Just click and read about these and other irons Mizuno makes.