Ryokan in Hiroshima
 

Looking for a Roykan to stay at in Hiroshima.

Its our first trip to Japan and we want to try a Roykan.

Looking for a triditional place to stay.

Other then that staying at Hiltons in Oska and Tkyo. Thanks god for points and Diamond status.

Check out www.japaneseguesthouses.com
My friend and I used it to book ryokans for almost every night for our 10 day trip to Japan.
They are very helpful and act as a liason between you and the Ryokans, since they usually do not have their own online booking.

Standard advice: don't spend the night in Hiroshima, but in Miyajima instead. Much, much nicer.

I'd also recommend visiting Miyajima first and only then Hiroshima: the museums and memorials are educational and informative, but sufficiently depressing to spoil the rest of your day.