XDs and M&Ps are fine pistols, but neither have proven themselves to the level that Glock has proven itself, but I expect the XD and M&P to be around for the long run.
If I weren't already somewhat invested in Glocks I would give the XDs a go. I have shot them and liked them. I have a M&P on T&E, but it just won't run well for me. It's VERY accurate, but the trigger reset messes me up, and several of our other instructors as have some others that I know.
I gave a couple of different 21SFs, a 34, a 17, and my own 19 a good workout today.