Your thoughts on vented vs unvented crawlspace – pros & cons – GreenBuildingAdvisor

I’m attaching 2 images from the DOE website showing a vented and an unvented crawlspace.

What would you consider the pros and cons of vented vs unvented approaches? 

One question about the vented option. It shows 1″ of polyiso under the floor. The ratio of polyiso to batt looks to me like it could result in condensation on the top surface of the polyiso. Is it best to respect the polyiso/batt ratio we would use in an unvented roof? Is there some way to eliminate the polyiso completely, like perhaps by taping all the floor sheathing joints so that the sheathing acts as a semi-permeable membrane as well as an air barrier?

Lastly, I’m not concerned whether the unvented option uses spray foam (shown) or rigid foam. That’s a separate issue. Thank.