There's a few differences between the two and it really comes down to preferences.
I've always found the Q701 much warmer and fuller sounding than the K701/K702.
The soundstage also felt more accurate for whatever reason.
There's a few other differences I've found and it's in the first post of the Q701 thread.
Also..sometimes the Q701 is cheaper for those inside the USA. Not always..
Really wish my stupid 65th pads would ship already. It's taking forever!