One factor to consider is whether you want adjustable or fixed sights. I don't think either of the Ruger 3" SP101 or GP100, or the J-frames, have adj. sights; whereas the S&W K and L frames at least come in both.
Another factor is the trigger. I have found Rugers with very smooth triggers and Smiths, mostly L-frames, with gritty monsters. I would check out specific examples and tend toward whichever ones had the best trigger for me.
I would lean toward the SP101 having owned it and J-frames and K-frames. I just like the compact robustness of it. But the Smiths are fine guns too. You really can't go wrong with any of them in my opinion.