This is going to be an objective comparison of the Glock 26 and S&W M&P9c. There will be no opinions in this piece; only facts and numbers. I think most people can agree both these pistols fill the same niche, as is evidenced in the below linked thread (despite not many people responding to the question):
They are both sub-compact, double-stacked, 9mm pistols whose primary purpose is concealed carry and personal defense.
Now let's take a look at the numbers (numbers pulled from genitron.com except for height and trigger pull which were pulled from glock.com and the S&W forums):
Barrel Length: 3.46"
Weight: 19.75 oz
Trigger Pull: 5.5 lbs
Capacity (flush magazine): 10
Recoil Rating: 6.79 ft/lb
Barrel Length: 3.5"
Weight: 23.2 oz
Trigger Pull: 6.5 lbs
Capacity (flush magazine): 12
Recoil Rating: 5.79 ft/lb
It is my understand that both guns can be ambidextrous in the sense that their magazine release buttons can be switched to either side. The M&P9ccan come with a thumb safety, but not every model does. Both the Gen4 Glock and the M&P have interchangeable palm swells. Some M&Ps can have magazine disconnects (rending the weapon unable to fire unless the magazine is inserted), but again, not every model does.
So, as we can all see, the Glock 26 is a slightly smaller gun in every dimension. Some would argue the difference in size between the two guns is negligible. Others think it makes all the difference. The M&P has two additional rounds, and has slightly more features that can be chosen.
Reliability? Both guns have had numerous torture tests done to them. Some of these tests have been over 100,000 rounds with minimal cleanings. I personally would trust my life to either.
In the end, neither pistol is inherently better. Better is a subjective term at best, anyway. We would have to define what "better" means. To some, the M&P is better because it has two additional rounds. To others, the Glock is better because it is slightly smaller. Ergonomics are also a subjective thing and cannot be measured objectively, so I didn't talk about them. Also, there are virtually the same amount of accessories for each, including 30+ round magazines.
So which do you guys prefer? Personally I'm an M&P man, but if they didn't exist and Glocks were the only polymer framed gun that filled that niche, I would own a 26.