Both good weapons. How much is the difference in accuracy worth to you? With the XDm I can shoot groups equal to what I typically experience with my 1911's that I can't match with the my XD's.
I have a XD 9 that I put a Storm Lake threaded match barrel in to use with a suppressor. Wow, now it holds groups as tight or tighter than the XDm 9mm. The cost to upgrade the barrel + the original cost of the XD was greater than a new XDm even without the threads.
However, I like the XD grips better.