I got a highly modified JBL Comp XHD and works great, last week I got a 3.5 pound Capitan and some 9 pound groupers have made it to the BBQ due to this gun.
Parts are rarely needed and readily available in my area, I've been using JBLs (former Voit AMF) for 25 yrs, I know isn't the best gun in the world, but budget friendly and last for ever.
If you plan on spearfishing every weekend or on a comercial way, then you probably would want a custom full blown WONG GUN, but to me, to have a $600.00+ gun sitting in my closet for weeks on ocasions, won't cut it so I prefer the JBLs.
AB Billers, are more or less the same quality as the JBLs, but I've never tried them, thou I've only heard good things about them.
In the Wood vs Aluminum issue, the vast majority concludes that wood is better than alum due to bouyancy.
Avoid the pneumatics, too much trouble.