The most famous city for Okonomiyaki is Osaka. It's local specialty of the region. Hiroshima is also famous for Okonomiyaki, with their own style Hiroshima style. Hiroshima style adds noodles and fried egg on Okonomiyaki and sauce is a bit more watery comparing to Osaka style.
Those are eaten at Tsukishima in Tokyo.
There is a store of many Okonimiyaki and Monjyayaki in Tsukishima.