Walter once bubbled...
Free shafting is not having a line attached to your shaft. Some prefer it because they feel the fish will feel the line and put up more of a fight.
Walter, hate to correct you, but that's not why people free shaft. Free shafting has become VASTLY more popular on Florida's Gulfcoast, especially with the popularity of the Commercial Gun made by Spearfishing Specialities.
The logic behind freeshafting is this:
1. Safer to diver (and to other divers who may be down with you);
2. If you become an excellent shot, a line should not be necessary, as you learn to "stone" or "brain" fish with regularity;
3. Greater range, not being connected to a line;
4. And, cited most often as the reason for free shafting: SPEED. Quicker to reload and take another shot.
Some free shafter have acquired sufficient skill to free shaft larger fish, such as amberjacks and cobia. I have done this, and if you don't stone the fist, it's is a major pain "running" after him and getting control. Some guys can routinly hit an AJ and turn out the lights right away.
By the way, Riffe is now apparently recognizing the increasing popularity of free shafting, and has started making an optional "enclosed track" for it's guns, which permit free shafting a Riffe. I would point out that Jay Riffe told me, "If you bend your shaft, your done" for that dive.
To the original question: There are two guns I primarily use. First, I have a Riffe Metal Tech 3 line gun. I use it in primarily two situations: 1) The bottom of the ledge or structure is deep (e.g., 130 ft or more), and I don't want to have to swim to the bottom to get my shaft; and 2) I am planning on targeting amberjacks only. I might also use it if I know the stucture has a very deep lip, or has cave type holes that would make retrieving an injured fish difficult.
My second gun, and the one in use 90% of the time, is a Spearfishing Specialties Commercial Gun w/ spare shaft. I use this for free shafting fish. The negative on this gun is it's expensive (around $500 - $600). But that's about the only negative, and I think for this area of the country it's hard to beat, IMO. It's all a matter of preference.
Scott