The amount of nerve damage it actually does is sorta still in debate. But naturally, that's nothing to mess around with. Besides, polyester resin smells just horrible, and when you wear a cartridge respirator, you can't smell it at all. Personally, I like being able to work indoors, so I nowadays spend the extra money and use epoxy resin.
As far as Gel-coat, it is mostly the same as polyester resin. It is different in that it is thixotropic, which is a fancy word meaning it is thick in such a way that it stays where it is put. Finally, it is waxed, meaning it has wax dissolved in it that rises to the surface as it cures. This wax forms a protective barrier from oxygen, which prevents the surface from fully curing.
Waxed resin isn't all that critical if you plan to sand and paint the surface. So when I need thick resin, I just mix together polyester resin and autobody filler putty (often just called "Bondo"). I get more control of the thickness, and it tends to be a good deal cheaper.
As far as which method is better as it relates to end appearance? Well...it doesn't. The end appearance entirely has to do with how much work you put into the process of surfacing; all the steps that go into getting a smooth surface; sanding, filling, priming. Particularly when new at the process, you can expect to either spend dozens of hours sanding and filling and sanding some more, or getting sick of the process and throwing on a coat of paint, only to notice all the little bumps and layers and textures that you could barely see before. With practice, and maybe a couple power tools, you can get the process down to a couple hours.