Having placed and restored thousands of implants and all-on- 4/6/8’s, zirconia porcelain is the best. My experience with acrylic is that teeth often pop off or break resulting in multiple visits in the office. Plus zirconia is more sturdy and will last you for years and years. Acrylic is like the tires on your car and wear and tear with use, eventually you would have to replace you prosthesis all together (5-10 years).
Full implant mouth rehab is usually done on people with a lot of bone loss. The upper maxillary bone is softer than the mandible hence more failures. The more over engineered the better as far as distributing forces and in case of implant failure the prosthesis has opportunity to still be used, had said that if possible more than 4 implants ia always better (5,6,8). As far as the prosthesis forget acrylic hybrids! Teeth pop off or break, they wear off and pink acrylic will break with time. It is better to use zirconia porcelain, you will be happier with your results!