I have a pair of the KRK RP-8's. I listed to them and several others in the "Prosound" section at Guitar Center (obviously not the best place to A/B speakers) and I picked them because they sounded good, I liked the shaping controls on the back, and the yellow cone looked cooler (silly I know, but what the hell I like 3's).
I have heard people say that KRK's are flatter and I have heard people say that the M-Audio's are flatter. I don't have the actual answer there.
As far as quality, one of the two monitors started generating some sort of digital distortion, but only around the frequency of a "D" on a bass guitar (standard tuning). I contacted KRK who were in the process of moving offices, so they had me send the speaker to some joint in CA.
They "fixed" the speaker and returned it to me. I plugged it in to find the problem was actually worse. I called KRK ready to tell them to shove their speakers where the sun don't shine, but the dude must have felt the negative vibes because he told me to send the speaker to them, on their dime this time, and they would repair or replace it. A week or two later, I got a new speaker.
So while it took two tries, and I received no real communications from them during the process, they did honor their warranty and replaced my speaker and overall did right by me.
Also, I wonder if they are getting near end of life on the Rokit line as they have come down in price since I bought mine just over a year ago.
I know you asked about different speakers, but I hope a little background on the manufacturer might help in your choice.
-Wes
