The most underrated class i have seen is Monk. All Monks even Unchained seem to be underrated. I find that with Ascetic Style (unarmed damage on all monk SQ weapons) +Ki steal is more than most GM's I've ran into can handle.
On a side note, though it allows it in the rules never allow the Monk weapon quality to any Bows... a Unchained monk with a potential of 5 -2 BAB/-12/-7 (before haste) at lv.11 gets broken.
