When shopping for your first speargun it is essential that you first look at your needs for the time being. Now if you are a beginner and this is your first season as a spearfisher, you should get an intermediate speargun designed for smaller fish rather than the larger and more powerful spearguns designed for large fish.
Handling a speargun takes a bit of practice and if you are just starting out it would be wise to start light and to learn the workings of a speargun as well as how to steer it in the water before you go any bigger.
You must always remember that a speargun is a powerful and dangerous weapon and attention and discipline must be kept at all time while handling a speargun.
Although these tips are somewhat no-brainers, I feel that I must still mention it.
Never load a speargun on land!
Never aim or point it at others and make clear rules of your locations while diving.
You will find a large variety of spearguns and brands on the market. Some are made by more or less unknown brands, while others are tried and tested. Stick to the known brands and you should be fine with regards to quality and functionality.
As a new spearfisher you will be looking for preferably a 95 cm lightweight speargun with a single string (rubber band). This size will cover a wide range of sizes and will work fine for most spearfishers. This size is relatively easy to handle in the water and will still have a good kill-radius as well as being easy to load for even the smallest person.
As a beginner I do not recommend that you do any deep water hunting, and so you will not need a reel on your speargun, this feature is useful when hunting for larger specimens and in deep sea hunting where the fish might make a strong run for it after it has been hit. However, hunting for this size of fish can be dangerous and will require a skillfull hunter in order for it to be done in a safe way. Remember, there are some fish outthere that could go into a dive and have the strength to pull down the diver or at least keep him submerged.
Also, by attaching a reel to your speargun you add a lot of line that can potentially entangle a novice spearfisherman.
Once you feel safe in the water, and have learned the basic awareness of lines in the water around you and have learned to respect the strength of even intermediate sized fish, you can begin to plan for larger fish and deeper or more difficult areas. Patience and attention to detail is the key to safe diving.
Some of the known and tested speargun brands are Omer, Mako Spearguns, JBL Spearguns and Riffe Spearguns. Although other brands will also do fine, just make sure to read up on the particular speargun that you are looking for or ask your local spearfishing / freediving club for advice.