San-in or Shikoku?

I am trying to plan the last of our 4 weeks in Japan (this October) and it seems like its going to come down to a choice between San-in coast (and part of San-yo) or Shikoku. Our itinerary so far is:

Week 1: Tokyo-based (day trips to Kamakura, Ghibli museum, maybe Hakone)
Week 2: Matsumoto-Kiso Valley-Kanazawa
Week 3: Kyoto-based (day trips to Nara, Iga-Ueno, maybe Kobe and/or Osaka)

We know we'd like to visit Hiroshima and Miyajima but from there it seems like we need to choose between:

(a) San-in: Matsue, Hagi, Tsuwano (maybe Yamaguchi too), or
(b) Shikoku: Matsuyama, Kochi, Takamatsu

I should mention we're a family with 3 kids but they don't really require kid-specific sites - anything scenic, natural or with a good historical story is a hit with them. We have about 8 days before we need to be back in Tokyo for our flight home.

Thanks in advance for any help or comments!

. . . is just across the inland sea from Hiroshima, you'd have to go waaay south to Kochi. I'm not sure it's the same trouble to take in Tokushima, which has more to offer. If you intend to take in the Oboke Gorge area on the way to Kochi, that evens the score.

The San-in route is pretty compact if you don't take in Yamaguchi. There's a lot to see in the latter (it's underrated) and I would leave it out. Instead you could add Akihoshi Cave/karst area near Tsuwano. It's definitely one of the biggest - if not biggest- cave in Japan.

The southern Yamaguchi area of Shimonoseki, Ube, Hofu, and Yamaguchi is worth a separate trip in itself.

Thanks, I am leaning towards Shikoku at this point. Can anyone suggest what a good one week itinerary would be? We prefer to minimize one-night stays since we are travelling with 3 kids. We'll be arriving from Hiroshima and leaving at the end to Tokyo.

Thanks very much for any advice!

My favorites:

Kagawa Prefecture:
Ritsurin Koen
Konpira Shrine

Ehime Prefecture:
Dogo Onsen
Matsuyama Castle
Uchiko

Kochi Prefecture:
Kochi Castle
I also heard a lot of good things about Shimanto River, but have not been there

Tokushima Prefecture:
Iya Valley
Naruto whirlpools

A lot of these sights are introduced here:
http://www.japan-guide.com/list/e1107.html

Looks like there's alot to see, the hard part will be narrowing it down to a manageable 1-week itinerary.