Sustainable Solution is PROG PoW algorithm. Against ASIC's -AND- FPGA's. It renders ASIC's and FPGA's to only be approximately 1.1 to 1.0 or 1.2 to 1.0 better than GPU's in power efficiency and hash rate.
I don't think there is a single coin that has successfully managed to implement Prog Pow. The first that is able to do so will become incredibly popular in my view. The gpu mining community is larger and more diverse than the other types of mining.