Are chests > crates/barrels > boulders?

Yeah, I'd say... Chest > Boulder > Corpse > Barrels









In fact, I'd say...

Chest > Boulder > Act Boss with 241% IIR > Corpse > Barrels

Yes. Generally, the bigger the object, the greater quantity and quality of loot drops.

But of course you can get lucky and get nice things from barrels.

Found both of my Exaltes under rocks, back 2 back days. Then I hit a dry spell and found nothing but fusings alks and below for weeks.

random is random

I found under a boulder today.

A week ago I had 2 yellows drop out of 1 barrel when I smashed it. I break everything looking for loot.

I only bother checking what's inside chests and boulders, since those are checked instantly, unlike barrels, corpses and piles where your character has to do the stomping animation.
Not so sure about corpses now that I think about it. But I definitely don't care about barrels or piles.

got an exalted from a rock, its always worth it to open all