What would you chose and why?

[Paul]

Why are you thinking temporary shelters or is an alternative life style you're really after?

Come a general collapse or catastrophic event, I'm still going to be looking for permanent structures.
Bug out of not, it's better to hide than pop up somewhere unexpectedly and raise a temporary structure.
Locals would notice a new addition where they might not notice a forced lock.

Consider the advantages.
Most structures are built with two things in mind, keeping the weather out and offering some sort of security.
Once in they may have resources you can use.
Most structures have been built for a reason so they'll often have approach roads and the like.
Good for you as you'll not be leaving new tire tracks on virgin soil.

Any disadvantages?
You may have to raise a smaller structure inside to live in BUT with the additional weather proofing of the main structure, it is infinitely better than living in a field.
Someone owns or owned them.
They're logged and listed somewhere.
In a systematic search, they'll get to you eventually.

Despite that, it's easier to walk away from something than transport large heavy equipment round.

Anyway that's my tuppence worth.