I usually use the Kodansha maps when in japan but for my last trip I was coming from the US and all my maps, notes, basically 8 years worth of "Japan" stuff was in my apartment in Sydney. Oops. I figured bare minimum I needed a map and it wouldn't hurt to have a bit of a guide. Since I had an older lonely planet at home I figured I might as well get the rough guide, at the least it would give me some maps.

While the Rough Guide was fine when in the major cities I thought it was really quite poor once outside of the major centres. Actually, the overiding impression I got was that they had never been to many of the places they were writing about. There was the odd "fact" which was incorrect but more common was that for a number of places they were missing what I felt was fairly vital information. I've travelled in japan a bit and have some basic japanese so could figure things out hiwever I think a first timer or non japanese speaker would have really struggled. If I had the choice of the two it would definately be lonely planet.

That said, I prefer to use the kodansha atlas's and my own research, I hated moving around the place and trying to plan things without a proper map.