I have owned and shot both. The 686 is a more "finished" gun with a better trigger (in general). The GP100 is a well made tank that will stand up forever even with the hottest loads. They are both excellent revolvers in my opinion. Personally, I prefer the 686.
I own both 6 inch models and yes the d.a. trigger on the 686 is alittle better, but is it worth paying about 100 or more $$ is something to think about. Both models great guns you can't go wrong with either.
I've got both and they're both great guns.
Both of mine have good triggers and shoot equally well.
I might have to give the edge to the Smith for having more grip options and probably better resale value.
Glad I don't have to pick just one.