Blackhawk Serpa has a finger release but has been blamed quite a bit lately for causing guns to fire a round when drawing. IMO I would blame partial user error but the jury is still split on the Serpa being both incredible and dangerous.
The M&P 9c is nice size but doesn't fit well in my large hands. If yours are as big as mine I'd recommend the Glock 19 or Glock 26 as the palm swell fills my hand just right. I do believe the M&P 9c has extra backstraps though I would definitely get my hands on one to make sure it fits before...