I prefer shooting in color (raw with most cameras) and converting to B&W over pretty much any in-camera B&W filter (even the wonderful Ricoh HiBW setting). So, both are excellent for shooting B&W. The differences are what you'd expect - the X10 is cleaner at higher ISO than the LX5 and that translates to B&W just as with color. I have plenty of B&W results I'm very happy with from each camera...
-Ray