We visited Iza Ramen, a weekend popup at Blowfish Sushi on Bryant, in late December. It's a pleasant place to spend time when it's not packed to the gills and noisy. Chicken karaage was well done, not greasy, served hot. Tsukemen was a bit unusual; instead of a small bowl of really intense dipping sauce, it was a medium-sized bowl of somewhat concentrated broth, slightly vinegared. The broth was really good; noodles and toppings were solid. Overall probably the best ramen I have had in SF, though I do not have extensive experience. (I don't have a car to make South Bay pilgrimages, alas.)
I had a weekday lunch at Ramen Yamadaya in the pedestrian mall in Japantown. I ordered the Yamadaya kotteri, which comes with extra toppings. The broth was not too rich (I remember a kotteri in Kyoto that just about stopped my heart) and quite flavourful; chashu was good, as was the egg (they make a point of not overseasoning the toppings). There was a hunk of kakuni in the bowl which I thought was not up to par, the lean meat being too stringy and the fat not meltingly soft. And the noodles were disappointing: thin Hakata style, which I don't care for as much, but even given that, they were too soft and flavourless. Overall still good, but no match for Iza, and not as good as I remember Kirimachi being.