I prefer a tiled shower, and wouldn't use any of those. For a tub replacement, www.schluter.com makes two different tileable pans for use with their Kerdi shower system. One has the drain centered, and the other has the drain at one end. Note, all showers require a 2" drain in the USA, so you'll need to redo the drain up until it is at least 2", so you could either leave it about where it is or move it. Schluter has some videos on their site showing how one of these goes together. For tiling help, check out www.johnbridge.com.
I would not use fiberglass and, if not specifically precluded from using it, I'd make sure to set the shower pan in mortar to give it full support. If you use the Kerdi pan, you use thinset to anchor it to the floor.