A matter of taste. Prefer the XDS to the M&P shield. I just shoot it better. I also like the short clip for CC. Extra mags are the long ones.
Both excellent guns, but the XDS is manufactured in Croatia, and the Shield is made in the US.
What really pissed me off is, as soon as I bought the Shield, they came out with it in .45. Only a tiny bit bigger. I may have another 4473 in my future.