This is not necessarily a meaningful comparison, because they were very different people. However, I'll go with Einstein, because his intellectual contributions included complex, well-structured and worked out theories that required intense thought over a period of time. Tesla seems to have had a brilliant intuitive grasp of the nature of electricity, but his output consisted of scattered applications and experiments. He doesn't seem to have had organized a coherent theory of electricity based on his understanding. However, it's hard to say what his level of theoretical understanding was, as many of his journals have disappeared.