The smoothest double-action trigger pulls on average will be found on older Smith & Wesson revolvers that were made before about 1948 and had what are known as "long actions." The "long" refers to the distance the hammer moves through an arc before it's released and falls. That, and Smith & Wesson's hand craftsmanship and extra polishing that went into the lockwork
before the parts were case hardened is what makes the difference.
The practice of keeping the original mainspring but using a lighter one in the rebound slide is not always a good idea. If the trigger's return stroke is slowed one may short-stroke the trigger during fast double-action shooting and tie up the gun. These two springs (main and rebound slide) are balanced with each other for a good reason.
When you reduce the mainspring you also lessen the firing pin's impact on the primer. Any time you reduce the pull below 8 pounds (10 is better) you risk misfires. If you are in the process of shooting a fast series of shots in the double-action mode and a light hit causes a hang fire, but your finger doesn't stop the next shot will likely be a double one, and you'll blow up the revolver. A total dud is one thing. A hang fire is an entirely different matter.
An ultra-light trigger pull is not necessary to accomplish pinpoint accuracy. Back when, using long-action S&W revolvers, Ed McGivern could flip a quarter-sized washer up into the air, and hit it while shooting double-action.
He made the point of explaining that none of the springs in his revolvers were altered. None of us are likely to get that good, but most could get "good enough" if they learned the proper techniques, practiced them, and spent less time worrying about the springs in their guns.