It just depends on what you're wanting in a gun. If you want 100% reliability then you have chosen two great guns to compare. Glocks are highly renowned for their reliability but as of date I have only had 1 malfunction with my smith (with serviceable ammo, of course). The smith should have a similar "safety button" on the trigger, the trigger has two parts, you have to press the bottom part back to squeeze the trigger.
In my opinion, Glocks and the M&P are the same(smith designed the M&P off of the glock). Similar features, similar safeties, similar design. The only reason to choose one over the other is personal preference. I think the glocks are ugly (why do you need a pretty pistol to defend yourself?) and that they just don't feel right in my hand, so I went with the smith.