Jbl 38 special comes right to mind but only because that's what i use in short vis and hole shooting situations aka grouper and snapper hunting. Again however, makos are top notch and if i had it to do over, i would have had a short closed muzzle mako first. Air guns are cool and truth be told they are stronger inch for inch, but, most people like band guns from what i can tell, never had a air gun so can't comment.
What's the vis like normally? Never any jacks or other bigger fish up over your structure? How big of a grouper do you want to gear for? You can shoot lil fish with a big gun but no shooting big fish with a little gun...
Even so a jbl will pretty much get it done, dialing in length is preference mostly just be sure to bring enough gun because wounding fish is a big no no to spearos.
---------- Post added May 6th, 2013 at 07:26 PM ----------
Just to clarify, when i say makos are top notch, i mean if you look at performance, price, durability and customer service, nothing is even close. The guns are lasers.
Are there guns out there that are better? Yes.
Do i always use a mako? Nope. I have a custom hand made bamboo gun, all metal mech and a magnet in the muzzle to hold my shaft down while freeshafting, it also has a single wrap of mono with a slide ring that let's me go from freeshaft (using no line) to a tethered rod in a few seconds.
If i didn't have my super bad ass bamboo gun then mako would be #2.