Fiberglass was until recently the most expensive type of pool you could get but the price of 'crete has gone through the roof so it is now a cost effective type of pool. IMHO, they are the best kind IF you find a shape and deign you like. (San Juan pools probably has more different models than any other manufacturer, including ones with beach entries, tanning ledge, negative edges, and built in spas) but that is not usually THAT big a problem.
Fiberglass a non reactive surface so water balancing is MUCH easier and chemical consumption is much less. Also the gelcoat last quite a long time so maintenance costs are lower over the years (no vinyl liners to replace, no acid washing and replastering. These are all normal maintenance for both vinyl and 'crete pools and either will cost in the thousands when they need to be done. Liners are usually good for 7-12 years and acid washing is usually needed every 3-5 years and replastering about every 10-15),
The ONLY reason I would suggest 'crete is because you want or need a custom design (perhaps your space does not allow you to put in a fiberglass pool) or because you are so far from a factory that the shipping costs on the fiberglass pool become so great that it's just not cost effective.
As you can tell I like fiberglass, which is why I has one installed, and have not regretted it. It can give you a pool that is much more maintenance free.
Algae does not stick to the surface like it can with 'crete so it is even less of a problem.
There are really only 2 downsides to fiberglass. One is that it is more prone to staining, particularly iron staining but removing the stains are fairly easy. vitamin c takes care of it! (I do need to treat my pool yearly to keep it stain free.) The second is that fiberglass pools CANNOT be drained without special precautions and maybe bracing since they can either pop out of the ground (but so can 'crete pools) or they can deform and warp. However, vinyl pools can't be drained completely either because the liner will wrinkle! In actualy use this is very rarely a problem since the usually reason a 'crete pool is drained is to acid wash, replaster, or paint. None of these are needed witha fiberglass pool.
Finally, some people object to the white color of most fiberglass pools but then again if you look at my avitar you will see that the water looks blue even though the pool is white (And if you put in color changing lights the night time effects become spectacular!) remember that many people do use white plaster in 'crete pools. Also, many fiberglass manufacturers are now making colored gelcoat on their fiberglass pool so this is becoming a non issue for those that WANT a colored pool (personally I prefer the white).
I can also tell you that my customers with fiberglass (AND vinyl) pools have much more stable water chemistry and fewer water balancing issues than those with 'crete pools.
Here are some pics of my pool.
I resemble that remark! See if you get a birthday card this year! 
btw, Waste, thanks for all your help on TFP 
that Joyce and I did does not 'turn you off' of this site :!: I know that I was unable to fully answer your question, but I gave you the best advice I could, given my very limited experience with fiberglass pools 