I have both (although my N is a 27 rather than a 28), the Rugers being Security Sixes. Having lived with both I would have to say this is a tough choice.
My 27 is the last personally owned duty revolver I carried. It retired pretty early on because we went to issued S&W 4" 66s which were mandatory carry.
I had chosen the 27 because I thought the N frame was the most rugged revolver I could carry. If the Ruger was in production then it was so early that it was not on the radar screen, at least mine.
Going from the N frame as a carry gun to the K frame was a great step up in comfort since it rode on my hip 8-10 hours a day (night actually). I also liked the shorter length of pull (LOP) for DA. I have large hands but not really long fingers. Conversely though I much preferred the LOP on the N frame for SA pull, which is what we used on the 50 yard line back then.
That was about it for the benefits of the K frame. We had a lot of problems with them. Quite a bit later I went through the CA POST two week rangemaster course and by the time I finished I was on my third 66. I had advanced enough in rank by the time the L frames came out that I was able to obtain them for my patrol division. My thought at the time was that the L frame split the difference between the K and N frames. More the ruggedness of the N frame with the better DA LOP and more favorable weight of the K frame, and hopefully better reliability than the K frame. The L frames did all this, and to this day I think it is the best S&W .357 platform.
During this time the Ruger was making a name for itself. I had my PPC gun built up on a Ruger. As I advanced in PPC I converted to DA only for the whole course. That made DA LOP much more important than SA LOP. I used that Ruger in competition from '77 to '84 when various occupational responsibilities forced me to give up recreational shooting (which competition was). I still have that revolver.
Despite our experience with the K frames, one variant of which I was fond of was the 2 1/2" 66, which detectives and command personnel could carry. I decided I wanted something of that configuration for my own. Given our departmental experience with the 66s and my experience with my Ruger PPC revolver, I opted for a Ruger Security Six 2 3/4" bbl. I put on a nylon Hogue Monogrip, and a spurless hammer (since I had long since converted to shooting DA only on all my DA revolvers). Equipped this way and with me shooting DA only, this turned out to be an ideal revolver from the outset to the present.
I have long since converted to a semi auto for EDC, so revolvers are only for recreation. What I have found is that I more often take out the Ruger than the 27 for recreational (and some instructional) shooting. It just fits me perfectly.
One caveat in all this: I am not in a position to say which will survive longest with heavy .357 loads. Our issue load was the US Treasury +P 38 spl load, and that was all we could carry. Competition of course was 38 wadcutters. FWIW I don't recall any felt recoil difference between the issue +P 38 rounds I fired in department shoots relative to the 38 wadcutters I fired in competition, but my total concentration was on firing small groups. Given that we were precluded from carrying .357 rounds, I never developed an interest in firing stiffer recoil rounds which were/are harder on the revolvers. Years down the line all of my revolvers are in great shape. They have been ridden, but I can't say they have been ridden hard. One is left to determine one's personal priorities in this area, so take it FWIW.
So, which to choose. Very tough choice, and I think a very close call. I think you first need to determine what will work best for you in the types of shooting you will do. Given one poster's experience, if you will be shooting a lot of heavy loads the N frame should withstand those loads better, but I am not sure that is a settled issue. As another poster pointed out the appropriate revolver comparison is S&W K frame against the Ruger Six series, not the N frame. So, what kind of loads to you intend to shoot? The next important question is whether you shoot SA and DA, SA only, or DA only. That determination will govern which will feel most comfortable to you, will allow you the best trigger control, and will result in tiny groups downrange.
If these questions still result in a tie, then I submit you should decide based on condition. For me, I am glad I have both, along with of course, my L frame.