it depends on what you mean by underrated. some pros are well known and loved, but they get nowhere near the money they deserve. if thats your thinking, i would say lj. he's one of the top 10 rail and jumpers, plus he shreds pipe pretty hard, yet he still lives the life of a broke ski bum.
but in terms of progression that goes unnoticed, i would say its a tie between andreas and charles. andreas has been spinning both ways better than most people spin one way for a long time. i mean he did a right double 10 mute in reasons, that was when there were only a handful of people who could do that trick natural. he also murders urban, i mean he was doing pretzels on urban pretty much at the same time or before wallisch's superunknown, but for some reason people always credit wallisch with bringing pretzels into the game more. and charles invented a grab, does crazy rail tricks that were hated on a while ago, but now people can't get enough of it. plus he has always spun both ways really good too.