I have pondered this specific question many times and my answer goes outside of the choices. I would buy the pre-lock 686, probably a no-dash through a daash-3 or dash-4.
I don't hate the idea of more capacity than six, but I truly do not like the idea of less cylinder meat to make that happen. If .38 Special was all I
ever wanted to run from either then my answer is likely different.
I love my six-inch, 6-shot 686, but I can admit that I tire of it a bit after 100 rounds because there's a heap of weight hanging way out front. A four-inch would be better, but to my tastes -- it doesn't look nearly as attractive when it's a four-inch with the full-lug. It looks stubby to me.
Give me a K-frame heavy barreled .38 like my 10 or 64 and I can happily send 300+ down range with no fatigue.
And when I am in the mood to drop bombs, the 686 can handle it without too much punishment on my hands, but my six-inch N-frame Model 28 handles it
even better. Full-bore .357 Magnum from either my four-inch or even six-inch K-frame just imparts too much shock to my shooting hands. Not after 6 rounds, but before I get to 50rds it sure does.
I had just a short little dance with a revolver running moon clips and it was not the joy I had envisioned, so I feel like it was a "thing" I had to chase and experience and now I am over it. Never say never... but I have no desire for a moon-clipped revolver ever again.
But if I did... p) it would surely be .45 Auto and not a .357. It seems to me that a big part of the
advantage of the whole moon-clip idea is the fat, short and stubby .45 round. It's quicker in and quicker out and needs precious little help in alignment. That part is blurred when using a long and skinny cartridge.