To move to a fusion DEMO power plant after ITER, a Fusion Nuclear Science Facility (FNSF) is needed in addition to ITER and research in operating tokamaks and those under construction. The FNSF will enable research on how to utilize and deal with the products of fusion reactions, addressing such issues as how to extract the energy from neutrons and alpha particles into high-temperature process heat streams to be either used directly or converted to electricity, how to make tritium from the neutrons and lithium, how to deal with the effects of the neutrons on the blanket structures, and how to manage the first wall surface erosion caused by the alpha particle heat appearing as low-energy plasma fluxes to those surfaces. Two candidates for the FNSF are considered in this paper: normal and low aspect ratio copper magnet tokamaks. The methods of selecting optimum machine design points versus aspect ratio are fully presented. The two options are compared and contrasted; both options appear viable.