I have not compared the K10 to the 12MA, but I did have a K12 and 12MA side by side. I choose the K12, mostly for the better warranty. Both sounded very good to me. I did not gig with both, just set them up literally side by side in my home studio and plugged in.
However, I do gig with either a pair of K12s or a pair of K10s, and the K10s are very capable of keeping up with a loud band (two drummers) on a small stage. For larger or outdoor stages, I tend to take the K12s, but neither is likely to run out of power on you. Typically, I put one down by my vocal wedge, facing me, and the second behind me on a crate. It creates a nice field of perfectly audible guitar sound, and I've never heard myself better on stage. I used to run a 2X12 cabinet and add some fill in the vocal monitor before. This is miles ahead of that.
Just a comment about the "which sounds better" dialogue ... as someone who uses gear at home but also gigs regularly with it, it should be no surprise to anyone that whatever you are playing through -- FR or a "real" guitar amp -- never sounds the same way on twice on a different stage. To me, it became about being satisfied with the tone I hear back on the soundboard recordings (we multitrack every show) and having that be perfectly consistent show to show, which it is. At that point, I feel I can trust what I'm hearing off my stage monitors, as long as it's loud enough to hear. If it's not as bright as I want, or the low end is lacking a little on a given night, I just don't worry about it, because I know what's coming out to FOH is correct. It's miles away from worrying about whether or not the "real" amp sounds "right" in its setting, because that's miked and going to FOH wrong if it doesn't.
So, while there are some subtle differences between the 12MA and the K Series, either one can be adjusted to sound "right" for you. My tone is perfectly consistent on any stage, and in my home studio, at any volume. The fact that the QSC has a 6-year warranty and extensive service network in the US, as well as being manufactured here, was a big plus to me over the Verve stuff.
To sum up, I think if you're gigging regularly, either will work fine, but the warranty and availability of the QSC wins out. The K also is a bit louder, in my experience. If you're setting it up in your living room permanently, then you should pay more attention to listening to each.