I've got the factory, smooth wood thumbrest grips on my 4" bull barrel MK II. Makes for a beautiful little gun. I like the thumbrest grips because they (fairly closely) approximate the high-thumb grip I hold on a 1911, the guns I shoot the most.
I've also had Hogue wraparound finger-grooved rubber grips, those were nice too.
I've had several pair of Lett's grips, and for aftermarket Ruger grips, I don't think you can beat them. I think I may just wander over there now, myself ...
MRH