For jungle Mundo, is it better to build the Hunter's Machete into Spirit Stone/Crest of Ancient Golem, or Madreds into Wriggles? Or might he start cloth armor instead?

Bump!

machette, no question. Mundo really doesn't do that much AA damage so you aren't getting that much benefit from wriggles. SoAG on the other hand gives you a big chunk of health and a really nice tenancity bonus. That being said, spirit stone by itself isn't that great for Mundo; you are better of rushing Warmogs and then picking up SoAG as a second or third item.

Id say try em both.. cloth+5 and machette+5.

Like you say his autoattack is only about 1/2 his damage output, esp as you rank up Agony. Getting health regen ASAP thru max health and regen itself is the best way to go.
Rushing warmog is a winner and with rank5 agony he clears pretty fast. Esp with cleaver to soften up the big dudes.

Dont upgrade it IMO. If you do late game into SoAG as said above is the only really good one.

Machete+pots

Giants belt and boots.
If you want to get trolly build a Lindras next. Alternatively stopping in Guise is fine for some more dmg and hp.
Otherwise
Warmogs
Sunfire
Randuins

u should KEEP that machete as a SPIRIT STONE to increase your clear speed and only upgrade it once mid/late game rolls around.