I own both.
I purchased the G26 first. I've had it a little over a year. I obsessed over that gun for a long time, and finally put it on lay away. Paid it off the next day.
Anyway...what was my point?
Sorry...too much Mt. Dew.
The G26 and the M&Pc are both fantastic guns. I have the M&P9c. To tell you how great they are, I offer the fact that they both serve the exact same function, and yet I refuse to get rid of one of them.
In my opinion, the greatest advantage that the M&P9c has over the G26 is ergonomics. And that's a bigggg advantage. I shoot both guns great. They conceal about the same (I use a comptac CTAC). I have mags for each that have the finger extensions, but tend to carry and practice using the mags without the extensions.
The stock sights, IMO, are better on the M&P9c. But I've never liked the Glock stock sights anyway.
The reliability of both pistols has been spot on. I have about 3,000 rounds through my G26, and about 800 through my relatively new M&P9c. The M&P9c had to go back to the mothership for a binding of the mag release. It came back fixed and hasn't had a problem since. The G26 hasn't had the first hiccup. Not even a single FTE or FTF.
Both are made by good companies that have strong customer service records and lifetime warranties.
Hard to make a bad decision when choosing between these two guns.
That's my take. Good luck.