I don't have experience with the XDm, but I do own two stock service size XDs: a 9mm and a 45acp.
I also owned a M&P 9mm for about 3 months.
The trigger is exactly the reason I got rid of the M&P and bought another XD (the 45). The M&P trigger was long and heavy. The heavy is what I couldn't abide; couldn't break a shot without the gun 'jumping' from the trigger break.
On the other hand, I have no problem with the XD triggers, even though I am a dyed-in-the-wool single action 1911 kind of guy. While a little mushy, they are not heavy, break crisply, and have a decent reset.
In stock configuration (no smithing or kits), the XD has a superior trigger than the M&P, in my opinion. I've only handled a friend's XDm, but it too had a very good trigger. I couldn't fault the M&P for anything other than the trigger; I liked the functionality and ergonomics of the gun, but I simply refuse to own a gun with a poor trigger, and was not interested in putting more money into a trigger job.