It is pretty widely accepted that a coil spring is more durable than a leaf spring, but that is not what my main concern would be... I want the trigger pull to be great while still having the ability to set off primers dependably. If I have to change out a leaf spring from time to time, so be it, but so far none has ever broken. Other folks' mileage may vary. At this point I haven't been able to bring myself to convert a Model 60 to a leaf spring, but I haven't totally abandoned the idea either.
Froggie