Hands down, Skyline Trail at Rainier.  Scrambled down to the Nisqually Glacier -first time on a glacier.  Awesome hike; different eco zones every 20 min.  Also cool traversing across a neat steep snowfield.  

Close runner-up.  Sidewinder Canyon in Death Valley.  The first major slot side  canyon was one of the three hikes featured in the Movie "Find Me."