I just gave my sister a G17 Gen 4 and I have a M&P 9. The M&P 9 grip is more comfortable and has a natural point angle IMO. My sister has small hands and preferred the glock because it was blocky. She said it was easier to hold on to with two hands.
Only way is to hold both and see how the grip fits your one/two hand hold. Keep in mind, the M&P in the shop will have the medium backstrap in place so it can get smaller and larger. Not sure how the Glocks come from the factory.
As far as reliability, both have ate everything with no probs.
FWIW, I shoot tighter groups with my M&P. The stock M&P trigger is lighter and smoother than the stock 17G4. It's a big enough difference that I'd recommend the M&P over the glock for the trigger alone, especially if you are planning on keeping the gun bone stock.
If you go with the glock, make sure it has the most current recoil spring assembly. If not, glock will send you one for free. I never shot mine with the old RSA, so I can't comment on if the new one is better or not. But.... the new one ran like a champ!
