Having owned both I can probably offer a bit of insight.
I have found the MG to be quieter - especially the steering noise, and much more responsive to controls than the MK. Setting up the MG to work with a Lowrance HDS was dead easy and well worth the dollars. (MK will do similar with humminbird combo units)
The MK remote control has a display which enables you to see the speed setting of the motor / spotlock/autopilot etc, and upon moving to the MG it was one feature I missed. Now that I can see the speed etc. on the HDS it's no longer an issue.
I moved away from the MK as I'd owned 3 models, and all 3 had failed after 3 years or so. All of the faults were in the main board. I went to MG to see if they were a bit more reliable, but will admit I haven't owned my current Xi5 long enough to make a call on that.
For mine, the major advantage of MG over MK is that it is very quiet in comparison, that said, I haven't used a new model MK recently..
I really don't think you'll be disappointed whichever you choose. They are both worth the money.