My XD's are all Mod.2 models (I was a little late to the game), but I assume the Legacy models are just as reliable and accurate. I'm sure the Subcompact is a great gun, but I would advise potential buyers to compare the Subcompacts to the 4" Service models prior to purchase (if you can find either of them in stock anywhere).
With my build, I found that the thickness of the XD models was a bigger obstacle to concealment than grip or barrel length. It turned out that I could conceal the 4" Service models just as easily as I could the Subcompacts. I shot the Service models more accurately and enjoyed the full grip and added capacity. You can't go wrong with either model. If you can easily conceal the Subcompact, then I would go for it. However, shooters built like me may find the Service Model to be just as easy to carry.
You may not even have to choose. With what the XD's sell for, you could probably buy both models for the price of one Glock. That's how I wound up owning enough of them to do a full comparison.