Well, I held both the XDs9 and the Shield .40 today and compared them.
The M&P won hands down, it just fit my hand better and the XDs grip was too aggressive.
I will say that that the XDs trigger stood head and shoulders above the shield. It's not that the M&P trigger was terrible, it was just kind of indistinct and blah to me, but I will be buying the Shield. Maybe a trigger job and some night sights.
Life is hard; it's harder if you're stupid.