I own a full size XDM .40 and an M&P .40c. I thought the M&P felt better as a compact, but that's just me...you may have a totally different opinion. I like the fact that the XDM will give you a higher capacity. But, my M&P holds 10+1 so I by no means feel under gunned. I like the pinky extension that comes on one of the M&P mags for range shooting and keeping at home. I'm pretty sure that the M&P allows you to use their full size mags in the compact models, which will give you something like a 15 round capacity for home use.
"They're on our right, they're on our left, they're in front of us, they're behind us; they can't get away from us this time."
Chesty Puller, USMC, Chosin Reservoir, Korean War
"You cannot exaggerate about the Marines. They are convinced to the point of arrogance, that they are the most ferocious fighters on earth - and the amusing thing about it is that they are."
- Father Kevin Keaney, 1st MarDiv Chaplain, Korean War