Hi Johnnyman88, welcome.
We have several Hawaiian spearos that active on the forum, and local knowledge is key when choosing a speargun. So check out the Hawaiian threads. Blaiz, for example, has started several interesting Hawaii-oriented threads. The key thing, I think, is choosing the length of the speargun to suit the visibility you encounter. The Sumora website has a really good table with suggested sizes for different conditions.
From what I recall reading, Hawaiian spearos often go for a combination of features which are/were* fairly unique to Hawaii. Typically a moderately long euro-style speargun or South African style railgun (maybe 110cm?), often modified with an open muzzle (perhaps because Hammerhead are based there?) and often with 2x14mm rubbers - a combination that you rarely hear about elsewhere but which offers the power of a 20mm band with easier loading and the option to use a single rubber around reefs.
*Open muzzles have become popular recently, not sure if it is a fad or the shape of the future. I think the idea was popularized by the Hawaiians. Most of the SA companies now offer an open muzzle option as do some European makers.
I forget which brands cropped up in Hawaiian discussions, Rob Allen was one (Florida Freedivers carry those in the US) and maybe Sporasub? Rabitech, carried by Sumora are another South African railgun option. Mako is a new US railgun company which offer similar designs/products to Rabitech, sourced from Taiwan I think. There are several other companies that offer railguns (Orcas, Pelaj in Oz, etc.). Forum member JimDoes2You has supplied railguns to several forum members in the USA in the past. There are a lot of eurogun options too. Maybe something like the Omer Cayman series (Italian) or Beuchat Marlin (French) series might be appropriate. There are some very cool Greek guns too, suitable for large fish like tuna (Triagon?). Also lots of other French, Italian & a few Spanish options. I believe there are some South American brands as well but never see any detail [please post if you more info. on them].
There are also some speargun companies in Hawaii. I believe Hammerhead now produce their own railgun there. Also Daryl Wong produces high end custom designs. Most of the companies/people/importers mentioned above have contributed posts to the DeeperBlue forums in the past, including Daryl Wong & Rob Allen - for which we are very grateful.