The only reason to not get a 7 shot 686 is if you plan on using it for IDPA SSR competition. I take it you are not an IDPA SSR shooter, so get the 7 round cylinder.
The 7 shot cylinder is not weaker and it does not jam more. I carry a seven shot revolver every day (sometimes a five shooter) and have done countless drills shooting and reloading and have never had a problem. My 7 shooter is a Smith and Wesson 386 mountain lite, the same L frame as the 686.
I can think of absolutely no situation where a seventh shot will in any way hurt or leave one at a disadvantage (except for IDPA, which only allows the revolvers in SSR to hold six at a time). Anyone who says "tradition" or "it is supposed to be a six shooter" demonstrates a lack of an ability to think for themselves. BTW, anyone who may be unhappy with that remark feel free to post logical reasons as to why a 7 shot revolver is inferior to a 6 shot revolver.
I just checked and as of last week I no longer own any six shot revolvers. I have only Smith and Wesson revolvers and they are 5 shot, 7 shot and 8 shot wheel guns. The 8 shooters are my favorite to shoot at the range, here is one of my pets:
It is a bullseye gun, not a carry piece.