Summer itinerary

Dear fellow travellers, this summer I will spend a couple of weeks in Japan (first time!!), flyint to and from Tokyo, and I ask for your help and assistance with the itinerary. I wrote down two versions:

Itinerary A
8 August: Arrival in Tokyo
9: Tokyo
10: Tokyo (daytrip to Nikko)
11: Tokyo
12: Kyoto
13: Kyoto
14: Kyoto (daytrip to Nara)
15: Kyoto
16: Hiroshima and Miyajima (overnight on the island)
17: Mt. Koyasan
18: Tokyo
19: Tokyo
20: Tokyo
21: Flight back home

Itinerary B
8: Arrival in Tokyo
9: Kyoto
10: Kyoto
11: Kyoto (daytrip to Nara)
12: Kyoto
13: Hiroshima + Miyajima (overnight on the island)
14: Mt. Koyasan
15: Tokyo
16: Tokyo
17: Tokyo
18: Tokyo (daytrip to Nikko)
19: Tokyo
20: Tokyo
21: Flight back home

Which one do you think it would be better? Suggestions?

Thank you! :)

As you probably know, you are traveling during Obon, the peak of the summer holidays:
http://www.japan-guide.com/e/e2286.html

Accordingly, I strongly recommend to avoid traveling from Tokyo to Kyoto on August 12 and 13. And in the opposite direction on August 14 or 15.

Apart from that I don't think the order of places matters much, unless, of course, there is a specific event in a city on a certain day which you want to visit or avoid. There are lots of festivals and fireworks during these days, that can be worth a visit (because they are spectacular) or worth avoiding (because of the associated crowds and problematic hotel situation).

On another note, I strongly recommend to stay overnight at Koyasan, which means you should allocate a total of 2.5 or 3 days rather than 2 days to Hiroshima, Miyajima and Koyasan.

Thanks a million for you answer Uji!

I think I would go for itineray B, leaving the visit of Tokyo at the very end of my trip. This way, I will avoid (fingers crossed) the big traffic on the 12th and 15th/16th.

I will spend one night in Koyasan and then travel back to Tokyo the morning after.
Do you think 6 days in Tokyo are too much? Should I add a night in Osaka in between the travel from Koyasan to Tokyo?

Do you think 6 days in Tokyo are too much?

It depends on the person. But even if were to run out of things to do in central Tokyo, there is a lot to see in easy day trips from the city.

Should I add a night in Osaka in between the travel from Koyasan to Tokyo?

I think these are personal decisions based on personal preference and interest.