Have in the past had both 66 and 686's in 4 and 6 inch barrels. To carry a whole lot and shoot some... take the 66. To carry and shoot a whole lot, especially with .357 Magnum loads and especially if those might include ammo in the thermonuclear range... by all means get the 686!
Currently I own and adore my 4 inch 66... and my 6 inch 686... as well as my 4 and 6 inch 28-2's. I carry the 66 when I want a thumper on my hip while I'm out and about in the woods/fields. I carry it when I'm in the car on the road, in a hotel overnight. And I commonly have it on the desk in the office.
The 686 is what I carry when I'm going to do some serious heavy duty shooting... maybe practicing for a match, etc. In that thing... 2-300 rounds of even heavy loads is just no big deal. In SA or DA, that thing is like a scalpel, you can really cut something down to size with it in a hurry. And... it's strong, any normal SAAMI magnum load will work just fine.
The 28-2's... they are what no other manufacturer produces... .357 Magnum revolver that can handle anything in the manual... and then some! I know we are all supposed to not exceed the load recommendations of the manuals. And just for the record, I've always followed such instructions. However, once upon a time in a different place and time I had a Speer manual that had some very interesting loads in it. They were impressive of both ends of the barrel. The 6 inch 28 that I had was shot hard with a pile of those loads. Happy times! Happy time! Of course now I have moderated things a bit. And for some reason I let that old Speer manual go... we were moving. We could not keep everything. Some of my books had to be left... Had to leave Keith (Hell I Was There!), the Speer manual as well as a lot of other things. Oh well. Last year I found and bought a new copy of HIWT. Doubt I'll buy another of that old Speer manual. However, the 28's... the 686... the 66... they will be staying a long long time. And of them all, probably the 686 is about ideal for a .357 Magnum revolver. If you ever get a yen for a little experimenting... you'll probably want to get a nice 28... they are made stout. Like a Timex, they'll take a licking and keep on ticking! JMHO. Sincerely. brucev.