Where are you fishing, the Med? Depends on what you see to some extent; for fast moving fish you would likely benefit from a shorter, lighter, faster tracking speargun - my 2 main spearguns fall into this category - but for large fish at greater range you might benefit from a longer, heavier, more powerful speargun - my old RA railgun and new Apnea Amorak rollergun fall into this category. Or compromise and go for something in between perhaps (100/105/110cm or long and fast tracking, e.g. C4) or buy 1 of each perhaps but...
My brother, over the years, has acquired several shotguns but laments that now he has more choice he always has the wrong one in his hands when he needs to take a shot! That can happen with spearguns too. For simplicity, I usually just take the best all round speargun for a given day or conditions. But recently, I found I made the wrong call several times. Fortunately, I have usually been able to get somebody on shore to pass me my longer speargun when conditions turn out clearer than expected. But I recently started taking both spearguns in the water with me, one strapped to my float; it is a hassle but turns out to be worthwhile sometimes. I recently acquired 2 new spearguns, one quite short, 60cm, and the other quite long and powerful, 95cm roller. Too much choice now perhaps? I think the 60cm speargun might become my short backup speargun which I strap on the float when conditions are fairly clear (when I am holding my lightweight 90cm speargun or 95cm rollergun) - as my 75cm speargun seems a bit long for this (a pneumatic would probably be the optimum/most versatile choice for a short float-mounted gun though - or perhaps a short rollergun?). My lightweight 75cm speargun will likely remain my main general purpose, poor visibility speargun for Dorset and, occasionally, Devon (although Devon conditions have favoured my 90cm speargun more often recently). It might be my backup float-gun for very clear days - although equally that might be the 90cm speargun (long but also fast tracking).
How about an
Omer Invictus 100cm or carbon 110cm or an RA 100/110 railgun, carbon and/or roller/single or double band (1x16mm/1x20mm/2x14mm/2x16mm)? There are lots of other options out there of course. I like the look of the fairly heavy duty Cressi Pacific models (Comanche or Cherokee). Beuchat & Pathos have some interesting models. Savlimar Hero is getting a lot of advertising currently, state of the art. I bought an Apnea Amorak 95cm roller speargun last year, on 30% off sale from spearfishingstore.co.uk, I guess that would be an option too. I wouldn't start out with a roller though, too much weight and complexity/hassle for a beginner, it would likely take some of the joy out of it.