There is no single best film. The structure is chosen around the product, not the other way round, and the first question is always what actually degrades it — light, oxygen, moisture, aroma loss, or fat turning rancid.
A clear PET/LLDPE laminate gives strength on the outside and a reliable seal on the inside while leaving the product completely visible. Where light and oxygen are the problem, a metallised layer blocks both and gives a bright silver surface that can be printed over or left exposed. Where the requirement is the highest barrier available — long shelf life, aggressive aromas, high-fat product or export distribution — a high-barrier PVDC-coated PET or a dual lamination is the structure to specify. These do the work foil used to do, without foil's tendency to stress crack where the pack is flexed, creased or knocked about in distribution, and the barrier holds for the life of the pack.
Tell us the product, the fill weight, the shelf life you are targeting and how the pack will be distributed and stored, and we will specify the structure around it. Contact us with your requirement and we will come back with a recommendation rather than a catalogue.