Accelerators have become a key ingredient in HPC. GPUs had a head start and are already widely used in HPC applications but now are facing competition from Intel's Xeon Phi accelerators. The latter promise comparable performance and easier portability and even feature a higher memory bandwidth - key to good performance for a wide range of bandwidth-bound HPC applications. In this session we compare their performance using a Lattice QCD application as a case study. We give a short overview of the relevant features of the architectures and discuss some implementation details. Learn about the effort it takes to achieve great performance on both architectures. See which accelerator is more energy efficient and which one takes the performance crown at about 500 GFlop/s.