I've owned four Python's, one a blue one from 1964, and three of the 2020's, a 6" (since sold) and two 4" (yes 4.25...big deal) ones. I just got my first 686, a 4", -6 model I've been boring everyone about. I've only got about 150 rounds through the 686, so I'm not really up on it, but I've seen enough to rate it as VERY nice. It could be Smith and Wesson's Python.
So which would I get rid of? Well, a Python of course. I've got two of them, so I'd still have one.
But a more serious answer would involve "why" am I selling one? If I needed to raise some quick cash for a really serious reason, the Pythons would probably go on the chopping block first. They'd probably sell faster, and even selling them to a gun store would raise more cash than selling a rather mundane 686 would. If on the other hand, let's say I just wanted to reduce my inventory? The 686. It's not a gun I've wanted all my life, it's just a gun I wanted to try. And they're pretty common at the LGS, so if I changed my mind later on, getting another one wouldn't hard. I'd look for a 4", 586 though. So no sentimental attachment to the 686 at all. I do have some minor sentimental attachment to a Python, having wanted one for years, and finally getting a couple. That '64 blue one, was supposed to be that one, but I had to sell it when I lost my job at one point. One of the few guns I really miss.
As shooters I actually rate them about the same right now. The Pythons look better, but if one shoots better than the other, I'm not a good enough shot to tell it. Triggers are pretty much the same, maybe a slight edge to the Smith and Wesson, but not much. They both feel about the same. Minor details like cylinder releases, locks, sights and such don't bother me. I guess I don't think one is "better" than the other...Just different.