I do an X-Y with two SDCs for picking, and a spaced pair or mono for strummed parts.
The reason is that most of my picking parts are more prominent and the X-Y really fills up the stereo field and picks up all the details in the playing. I use mono for strumming because it's usually in a mix and I don't want/need it to fill up that much space.
But, as with most things, the technique is dependent upon the song and sound I'm going for.