All-on-4, acrylic or or zirconia porcelain?

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The acrylic option is usually for a more budget conscious person, but what isn't often discussed is durability.  Monolithic zirconium doesn't chip like a layered feldspathic porcelain but also is not porous like acrylic.  After 8-10 years, the acrylic tends to harbor a smell/taste that requires replacement in order to remove.  Zirconium does not.  Also, the acrylic will wear out over time, faster if chewing against porcelain or natural teeth.  Some places design the case with porcelain on top teeth and acrylic on the lowers, knowing that in 10 years the lowers will be replaced due to wearing out (similar to how tires become "bald" the teeth become very smooth and worn down).

There are two good options for prosthesis after All-on-4 implant placement. Both prosthetic options has its own advantages and disadvantages. It's better the clinician takes the final call on what is suitable for you.
Acrylic wrap around is very lighter and cosmetically appealing too, but it wears out slowly over a period of 5-10 years and needs only the acrylic part replacement, which isn't expensive at all. The titanium framework inside doesn't need replacement. People with poor bone quality, shorter implants and very elderly, I personally suggest acrylic hybrid as an option.
Zirconium porcelain prosthesis is definitely stronger and long lasting. They look natural too, but they are heavier, ceramic chip-offs do happen and it can also cause wearing-off of the opposing natural teeth or acrylic teeth many a times.But my personal suggestion is that for people who are more concerned about aesthetics and also younger age group should opt for this Zirconium Ceramic option.

The hybrid zirconia and acrylic prostheses actually have the following difference: zirconia prostheses are characterized by being the most resistant and aesthetic prosthesis material, however acrylic prostheses are also aesthetic and resistant but not the same as a prosthesis in zirconia
I can tell you that I have received patients in my practice with prostheses on hybrid acrylic implants that have been in the mouth for more than 20 years and are very well, but there are patients who have zirconia prostheses and do not last for 10 years due to lack of dental hygiene. 
The two treatments are very good and I recommend them both, but I also recommend the patient a maintenance with the dentist every 6 months. 

Choosing between zirconia or acrylic is not something patients can decide on their own. You should consult your prosthetic specialist. A prosthodontist , understands the material behavior and suitability in your situation.
Acrylic is preferred :
1. When bone loss is more, cheeks and lips are unsupported, wrinkles and folds are present, and prosthesis is required to provide support. 2. Acrylic has an advantage that additional material can be added with no risk of adding weight to the prosthesis, which is the case with crown. 
3. Acrylic can act as a cheek or lip implant in itself if your dentist feels the need to support your lips and cheeks4. Esthetics and looks : Although zirconia and ceramic look better in comparison to acrylic but new age acrylics with cross linked polymers have better strength and match nearly same esthetics.
5. Acrylic is also easy on teeth, doesn't wear the opposite teeth, unlike zirconia or ceramic. 6. If you already have ceramic or zirconia in your opposing jaw it's advisable that same or similar material be chosen.7. If you have less space (8-10mm)in each of your jaws for jaws it's better to use zirconia or ceramic as acrylic gets weak and can crack in thin sections( for acrylic minimum 12-14mm is needed).8. If your opposing dentition has denture in that case also it is advisable to go for a hybrid acrylic full fixed prosthesis. 9. Latest innovation is, one of the lightest material, PEEK polymer which is absolutely easy on opposite dentition.10.Repairing acrylic is easier. It's easy to achieve esthetics and it's durable than ceramic repair on titanium or zirconia framework11 . Average life is 7-10 years for acrylic and  zirconia framework.