Two completely different animals, the MB is for a very solid ball striker vs. AP2 is much more forgiving...both are used on the PGA Tour.

690 mb lol i prefer them over my 714 ap2 and ive hit all the 716 and the 690 still takes it home for me

I can't game the MBs but currently play the AP2s and love everything about them.

The 716 MB's are still forgiving for a blade because they raised the muscle pad on the back of the club compared to a few earlier years. I have a set in the X100's and one of the rangers at my course (not the best ball striker and in his 70s) hit my 7 iron with very solid ball flight and he said the same thing everybody else did at first that blades were too hard to hit. If you play blades it will make your swing better because of the great feedback you'll receive from the feel in the club head. However, the AP2's are very solid as well they will be more forgiving but if you like the looks of a traditional blade but want more forgiveness you should look into the T-MB's.

I have a combo set with both and I love them. 9-7 MB's & 6-3 AP2's. The MB's definitely force you to be a better ball striker as Collin said, and have helped me hit my AP2 long irons better. My MB's feel solid when they're hit in the center and I can feel exactly where the ball hit on the club face. My AP2's feel crisp when I hit the center but don't translate as much ball strike feedback. (Only by a small amount) Though, the AP2's feel like a rocket when you get them right.

So I prefer having both, I like seeing the tiny MB's behind the ball then I want a more precise shot and the slightly larger AP2's for the longer shots. Both have worked really well together and look brilliant beside each other in the bag.