I have both the MK II and 22/45. The MK II is a 5 in. bull barrel and is more of a target pistol, as its too heavy to carry in the field. I bought a 4 in. bull barrell 22.45 becuase its smaller an lighter. ITs plent accurate, although not as accurate as the MK II which has a Volquartsen triger, and obviously longer barrel, etc.
I prefer the grip angle of the MK II, it just points more naturally for me. I also prefer the heal mag release for this type of gun. That being said, for the field, my little 22/45 is fine and has operated reliably over the five or six years I've had it.