Tried the Sumire corn and butter miso ramen. Briefly, very good. Less briefly: The noodles are chewier than Santouka's, and you can decide for yourself whether that is a good thing. The broth is slightly spicy -- less so than Santouka's hot version, but definitely noticeable -- and the miso is less pronounced. However, it is very, very flavorful. Where it loses to Santouka hands down is the pork; Santouka's special pork is just miles above. The sweet corn makes up for it, though.
I recommend that ramen devotees try it and compare for themselves. The festival is still on for two more days and there's lots of other fun stuff going on in the store.