If you are looking at a DA .22 for training, then get the one closest to the DA centerfire you have, or are planning on getting.
I won't speak to the Ruger, I don't know it.
What I have is a S&W model 17-6, with 6" barrel and full underlug. IT has precisely the heft and feel of my model 28 .357. Rather spendy (in fact, it cost me quite a bit more at the time than my Model 28 did), but I don't think there is a finer DA .22 out there, short of a tuned target gun.
If you use a K frame, a K-22 would be the ideal training gun. Again not remotely cheap.
Quality DA .22s are never cheap. They cost just as much to make as their centerfire brothers (possibly even more), and their niche market means that there is no price break due to mass production.
On the other hand, you get a virtual copy of the centerfire gun, perfect for low cost training and practice. And they hold their value pretty well.
If you just want a good DA .22 for general use, there are several less expensive guns that will serve just as well, or in somecases, better (pocket guns, etc), but they are less expensive, not cheap.
Any decent DA .22 will give you practice, and help improve your overall skills, so its not a tragedy of money ill spent if you cannot get the perfect match for your "duty" gun in terms of size and weight. But if you are going to have to spend a considerable chunk of change for one, I think its best to spend what you need to, to get the closest match you can, even if its more than you absolutely have to spend.
After all, how many of them are you going to buy? Properly cared for, the gun will easily last your lifetime, and well beyond.
All else being equal (and it almost never is) bigger bullets tend to work better.