Short answer: They are both relatively equal. Do not be afraid of a non-modified 586 (no dash) revolver.
Longer Answer: Models 581, 581-1, 586, 586-1, 681, 681-1, 686 (no dash), and 686-1 were all recalled by S&W to change the hammer nose bushing because of the potential, supposedly when firing .357 magnum loads with softer Federal primers, to experience binding of the cylinder due to rearward expansion of the primer causing the primer to rub up against the hammer nose busing and/or the recoil shields thus retarding rotation of the cylinder.
If the revolver has been modified (repaired = hammer nose bushing replaced) by S&W you should find a M stamped on the frame opposite the yoke.
As best I can determine S&W will still make this repair - no charge for the repair or shipping as best I recall. It is fairly painless to deal with S&W. Hopefully another S&W Forum member can confirm if S&W still makes this repair.
Between myself, my father, and another relative we own at least 3 of these recalled models and none of us have ever had the modification (repair) performed on our revolvers and we've never experience any binding. One of use shoots a significant amount of .357 magnum and one of use only shoots .38 special. I shoot some .357 (a few hundred rounds through one of the revolvers).
My best estimate, based upon reading many posts about this question, is that other shooter have the same experience as I've had - i.e. in practical use there has been no problem without the modification.
The one instance I would want to get the repair (modification) performed is if I was using the gun for self defense and I needed it to be as reliable as possible.
If you were to get a non-modified revolver:
1. I would bet you'd experience what I suspect is the norm, i.e. no problems.
2. On the other hand if you obtain a non-modified gun and start experiencing problems then send it off to S&W.
3. Or, you can just send it off to get repaired (modified) if that's what suits you.