Unless you have a specific reason to stay in Osaka, I'd say you're probably better off staying all four nights in Kyoto and visit Osaka as a single day trip from there if need be. For a first time visitor, there is much more to see in Kyoto, and going to Osaka from there just takes half an hour or so anyway.

Actually, skipping Osaka altogether and doing a day trip to Nara instead (say) is an option to consider, especially if you're bound for Tokyo afterwards. Going all the way to Hiroshima is also possible but that would have to be a bit of a rushed day trip.