I never sell anything personally.
I think the question is which is the better gun? If you HAVE to get rid of one I wouldn't jump to the conclusion of "I have a glock" from what i've seen, my M&P has been just as or more reliable than a glock. Have more questions? ask a few police depts, ours here switched over to the M&P and never looked back, they say they are cheaper to maintain and purchase.
Don't know if that's an option for you or if you have some sentimental attachment to your glock, if not I'd say logical deduction > brand myopia