I can't (and won't) denigrate either brand as regards quality or reliability. But, I can make a few observations which I think are pertinent. I've had two Ruger SP101's, actually up until a few weeks ago...and through which I put, collectively, more than 1500 rounds. The first was a 2" 357 mag, made in 1994. The second was a 3" 38 spl., made the first year of production, 1989. The 1989 gun was certainly the better of the two.
One, the barrels on both the SP101's were over-torqued. The 2" gun shot consistently left, no matter what (and yes, I tried everything to make sure it wasn't me - it wasn't). The older 3" gun was much better, almost correct, but not quite.
Two, the chamber throats on both SP101's were absurdly tight, something like 0.355". So, I had to open both cylinders up to proper size to handle standard 0.357" dia. bullets. The barrels were OK, between 0.355" and 0.356".
Three, the forcing cones on both guns were cut at only about 5 degrees, which is fine for jacketed bullets, but plays havoc with cast bullets. I never found a combination that wouldn't lead the forcing cones. The 2" gun would lead up like crazy, even though the timing was spot on. The 3" gun would lead less, but still enough to be a pain. I polished the FC's on both until they shined like a mirror, but they still leaded. The FC on the 2" gun was incredibly long, more than 1/2" before the rifling started. The 3" gun had a more "normal" configuration. In retrospect, I should have had the FC's re-cut to 10 or 11 degrees.
I had no other problems with either SP101 - but those things were enough.
I ended up trading the 2" SP101 for an S&W 64-3 in great condition, which I converted to a 3" HB/RB (it was a 4" HB/ SB).
Shoots much better than either of the SP101's....and handles any loads I feed it, just like my 3" Model 10-8, without any issues. The barrel and cylinder dimensions on both of the K-frames are perfect for 0.357" dia. bullets....and very consistent with each other, at that.
I kept the 3" SP101 a while longer, then traded it for a 442-1. The 442 also eats any load (cast or otherwise) without issue. Again, the barrel and cyl. diameters are correct, right out of the box.
In fact, ALL of the S&W's I've had have been correct, "right out of the box", in this regard.
All of this PROVES nothing. But, it did make an impression on me. Not that Ruger quality is low, no, not at all. I would say the opposite. But, there was something to be desired in the QC, or technical design....if both guns, early production models but 5 years apart, both exhibited the issues detailed above.
I would not discourage anyone from buying a Ruger. As these were older guns, perhaps the newer ones are better (that was NOT the case with the two I had, though). I would simply offer a caveat for those considering a Ruger, an SP101 in particular. You should perhaps be prepared to "fix" certain details, in order to get the gun to shoot as well as many S&W's do, right out of the box.