Your choice of spearfishing equipment depends on the environment in which you will be hunting and the fish you want to take.
All of my spearfishing is done on wrecks, concrete rubble, and limestone reefs. Obviously the wrecks and rubble provide a lot of holes for the fish, but even the reefs have deep and narrow crevasses and overhangs.
My favorite fish are grouper, snapper, and triggerfish. I could use freeshaft on the triggerfish, but the grouper and snapper always "hole up" (I doubt that I "stone" a fish more than often than 25% of the time).
For me, freeshafting would be an expensive proposition. As a matter of fact, grey/black snapper tend to hide under ledges and in crevasses, so I will often take a shot that would guarantee a lost freeshaft, but is routine for a line shaft.
Lineshafts require the extra step of wrapping the line, but I'd be suprised if that step takes more than 15 seconds. On the plus side for (some) line guns, if the gun is negative with the shaft loaded and buoyant without the shaft, you can shoot the fish, let go of the gun (which floats above you out of the way), and concentrate on getting the fish on your stringer. With the fish secure, you just pull your gun down and reload.
You might want to read a book such as Spearfishing and Underwater Hunting Handbook: Beginner Through Advanced by B. Allen Patrick as you get started.