Thanks to all people who have commented. It seems that the real answer is "it depends". I think I'll try all Spectra with a 20 foot wind-on leader (fluoro) to the snap swivel and a short, 3 foot fluoro leader from the snap swivel to the bait or lure. I'm hoping that fish don't notice anything that is over 20 feet from its intended prey, and that the fluoro is really as invisible in water as its price suggests.
I'm also hoping that I don't hook into something that really needs a shock absorber. Although I like to fish with relatively soft rods, there is only so much the rod can do to take out the shock, and if the shock hits as you are winding down on the fish, the rod isn't going to absorb much of anything as it is more or less pointing at the fish at that stage.
However, the short fluoro rig will give me a rig that is good for bottom bashing, trolling and live baiting, which makes it very versatile. Let's see.
I have decided I don't want to fight any more marlin, for a variety of personal reasons, so that really eliminates the worst of the shock makers. Tuna don't make too much shock, and while Dorado (Mahi Mahi) can dish out a fancy dance, the actual load is usually not too bad.