I looked at the XD. Did not like the grip safety, high bore axis, blocky shape--but it is a good reliable gun.

The M&P 9c has the same grip width double stack as the Full Size. The grip is just shorter, so a little harder to use, unless you use an extended mag, in which case, carry the full size. The shorter barrel is not really necessary for concealment unless you pocket carry. However, there are devotees who love these compacts and shoot them very well. I would prefer and do carry a FS most of the time.

I carry my Shield as either deep concealment in Thunderwear or AIWB with a light covering garment (t-shirt). That's not too often, but because it is lighter and flatter it fits this role for me.

So the Shield is the second of two guns I carry. I don't need the in-between size 9c or XD, but if you only carried one gun, then it might be a good consideration because of increased capacity primarily.

Don't let cost persuade you one way or another. An extra $150-200 should be of little concern when making an important purchase like this. Get to a range if you can that rents these guns and spend some coin trying them out. That will serve you better than my or anyone else's advice.

If $$ is a big factor, then find which one you like and buy one used.