There are a lot of discussions about the pros/cons if you search.
Fiberglass is limited in size and shape. Install requires VERY good prep work. There is no easy way to refurb it. There are a few horror stories of fiberglass installs gone bad.
Vinyl allows for larger pools and more flexible with shape. Easier to do a DIY install. Easy to replace the liner as needed due to age.
A lot depends on who is doing the install and what is "normal" in your area. For example. I have never seen an in ground vinyl pool down here and only know of one fiberglass pool ... they are all plaster pools.
Where I am there seems to be a pretty even split between plaster and liner with fiberglass making some serious inroads. I have only had one pool and it is fiberglass. Despite the size limitations I am not sure I would have gone with anything else.
Ultimately I think everyone likes what they have and since each has their pros and cons, you have to decide what your needs are.