My kune kune pigs have been living on an area of woodland that had been felled and left to overgrow. There were brambles etc taller than me, and they've cleared it beautifully! They're still working on rooting up the tree stumps but are having a good go, many are loose now! Also it's pretty easy to work a bit of a path through the overgrowth to lay electric fencing to gradually expand the bit they're clearing, as pigs only need a couple of strands up to about knee height, where sheep and goats need more robust fencing.
I definitely wouldn't recommend sheep (I've had hebrideans tangled in far less), nor goats (in my experience they'll really pick and choose what they want to eat - my grass is good just now so the weeds- thistles, nettles, docks- are really growing in the goat field!)
Just going by my experience, I would recommend pigs for clearing that area.