I've been there a few times as I used to live close to Hiroshima.
To be honest, I will always prefer Nagasaki! The city has been through the same destiny, also has an atomic bomb museum, but seriously ... Nagasaki has managed to overcome what happened and turned into a beautiful and interesting city.
If anybody has the chance to choose I'd rather go to Nagasaki.
Hiroshima Castle is also not so interesting compared to others.
However, Hiroshima is close to Miyajima and thus always worth visiting after all.