I pretty much ONLY use the polyester hoof tape these days, because:
1) It has much better abrasion resistance than the fiberglass. So, casts last much longer, which is great for horses that move a lot and live on hard or rocky ground.
2) It's far more flexible/less brittle than the fiberglass. That means it can withstand a lot more flexion/distortion/etc without cracking, which makes it better suited for horses who move a lot and hooves that are prone to twisting (ex. hind feet, and front feet with angular deformities). I also sometimes come across horses who seem to resent having their heels constricted by fiberglass tape (perhaps it impairs shock absorption), and those horses tend to be much happier in polyester.

The only time I still use fiberglass is for horses who are moving very little, and horses who can't yet tolerate ANY flexion/distortion of the hoof capsule (ex. laminitic horses at the beginning of their rehab, and some navicular horses with a very weak and/or diseased caudal foot).