Shirakawa-go and Gokayama vs. Koyasan

if you had to choose, which would you visit: Shirakawa-go & Gokayama OR Koyasan.

I can't decide.
I think there is more to do in Shirakawa-go & Gokayama and the food seems good. buckwheat udon.

please advise.

I have not done the whole "staying in a temple" at Mt Koya but I have stayed in a gassho zukuri house at Shirakawa-go. I must say that the latter was one of the coolest things I've done in Japan, and I think I've done a fair share of things here. If you go during the autumn or even the winter, I imagine Shirakawa-go is even more gorgeous than when I went (late spring/early summer).

So, you are trying to decide between two fantastic experiences that many tourists don't do. Which would you rather do: spend a day/night in a World Heritage designated farmhouse in a remote countryside village nestled by mountains (Shirakawa-go) or spend a day/night experiencing Buddhism in what I'm sure is a very beautiful area atop a mountain (Koya)?

It's up to you.

I've stayed in Shirakawa and Koyasan. Both have their own unique experiences. Shira has those gassho houses and rustic setting that takes you back in time. Koyasan has the buddhist monasteries where you can stay and have shojin ryori meals. Visit the Okunoin cemetery where Kobo Daishi is entombed.