My hood! I've never been to Hiroshima any other way than by ferry, both high-speed and regular. I lie, I once went by car over the Shimanami Kaido but that was from the next city along from Matsuyama. This trip can obviously also be done by bus. Best bet is shinkansen to Fukuyama then bus over the bridge. I'm biased towards the bridge but for a real Seto Inland Sea experience the ferry is pretty hard to beat. Train? Talk about going all over Chugoku to get to Japan!