They have both shown equal intelligence feats so I am going to go buy academy graduation age. Itachi at 7 and Minato at 10. Itachi does have an edge by having the sharingan, which helps with his analytic skills. This doesn't mean anybody with sharingan could deduce a jutsu workings, so I'm going to give it to Itachi.
p.s. It takes some serious mind f***ing ability to get someone to position themselves in the exact same way twice (Izanami)
p.s. It takes some serious mind f***ing ability to get someone to position themselves in the exact same way twice (Izanami)