A dental filling should not be completely resistant to wear but should have a wear coefficient as close to the natural tooth as possible. In terms of hardness, the order should be (from softest to hardest) glass ionomer, composite, yellow gold, amalgam, metal and, finally, dental ceramics.
In answer to your question, Ceramic fillings are the most wear-resistant and inert filling material. However, do please note that the harder a material is the more brittle it is.
Dental amalgam is historical, the oldest of the materials. It has had a bad rep in recent times but, in my practice, I have seen 50-year-old amalgams that had not needed changing!
