N is the gold standard when it comes to a peaceful & dignified exit. Nothing even comes close (except for other strong barbiturates). N first puts one to sleep, and then to a permanent sleep. It's the best way of CTB, no doubt about it.
Yes, it's extremely bitter to taste and can cause one to vomit it because of the bitterness, but an anti-emetic should take care of that. I don't mind having to gulp down an extremely bitter solution if I'm going to have a truly peaceful & dignified exit.
Look at it this way. N can even be more peaceful & dignified than a natural death. Not all natural deaths are peaceful. Not everyone who dies a natural death passes away peacefully in their sleep. Plenty of people suffer a lot (e.g. a heart attack) during their final moments before their natural death.
N as a method of CTB is on par with those elderly people who are lucky enough to die a peaceful natural death in their sleep.
SN, on the other hand, is merely relatively peaceful. It's very salty to taste, causes nausea and vomiting even after taking an anti-emetic and causes a very rapid heart beat among other possible effects. All this can cause SI to kick in and/or lead to one being found and supposedly "saved".
SN is much cheaper and easily available compared to N. That's all. On all other aspects, N is definitely superior to SN as a means of CTB.
I have SN, but I really wish I had N instead. Those who have managed to obtain N are very lucky indeed.