I opted for fiberglass for my pool becuase it is non reactive, unlike plaster, so your water balancing is much easier.
Also algae doesn't stick to the smooth surface so if you get any it is easer to treat.
It is much more durable than vinyl and will last much longer than a vinyl liner.
It does not need to be acid washed or replastered like a plaster pool
The biggest drawback to fiberglass has been the price. It tended to be the most expensive type of pool you could buy. Now that concrete prices have gone through the roof it is actually becoming very competative and in many cases less expensive than a plaster pool. I had many quotes when I was having my pool built last year and the fiberglass came in second lowest (AND the quote included a heatpump and automation!)