What you plan to do with the revolver has some impact on which one you might want. I would not worry about one being stronger than the other.
686 SIX Shooter:
You have the choice of using speed loaders made by about everyone in the business. The 2 big ones for competition shooting would be the Spring Driven Safariland Comp III, and the Jet Loader.
If you plan to compete in Revolver Match's some Divisions require 6 shooters, reloaded with Speed Loaders, such as ICORE Classic, and IDPA SSR.
686 Plus SEVEN Shooter:
You are down to a couple Turn Knob Speed Loaders, the HKS 587, and the 5 Star.
For Revolver Match use you will probably be in a Division where you would be ahead using Moon Clips to reload with. The 686 Plus can be cut for moon clip use with no issues other than the added expense.
For general range use, and home protection either should work fine.
The 686 is on the large end of the scale for concealed carry. Some will feel the 7th shot is important to consider, while others will feel the use of slower speed loaders with the 686 Plus, makes the 6 shooter a better choice.
I fall into the SIX Shooter for better speed loaders camp.
My grail revolver after clearing the 3 Inch 66-2 from the list, was a 3 Inch 686, SIX Shooter. Not real easy to find, at a reasonable price. I ended up filling this spot with a 3 Inch Adjustable Sight GP100 Ruger for the moment.
Just some things to consider. The $20 difference in price is not enough to lose any sleep over. Get the one that suites your needs the best, then try your best to wear it out shooting it.
Bob