In my opinion the XD is easier to conceal.
In this picture the AO 45 is behind the XD40. The 45s barrel and OAL length about one inch longer than the XD.
In this picture the 45 is on the left and appears to be about a thick as the XD,
I sometimes carry the XD concealed (going to costco to lunch on the free samples and to the doctors) using a CrossBread Qwik Klip set up for cross draw.