I started a similar thread a bit ago...
www.canadiangunnutz.com/forum/showthread.php?791615-G17-or-M-amp-P9-or-XDM
Since then I have bought both G17 and M&P9. Both great guns! Like others have already stated... hold (and shoot if possible) both pistols. It really does come down to personal preference imo.
For me...
G17 feels better in my hand
G17 trigger feels better, better reset (out of the box) (Apex for M&P will fix that)
BUT i shoot the M&P more accurately for some reason... go figure.
I also like the fact that the M&P22 is a cheap alternative to practice with. Nearly identical to M&P9 besides the weight of course. Huge plus imo.
I highly recommend you purchase both pistols lol.