yellowstone is beautiful but prolly too crowded - glacier is amazing, but be prepared for chilly weather - grand teton is wonderful! lots of flowers and great hikes - redwood is good - yosemite is always a favorite - but i think the absolute best are the southern utah bunch: zion, bryce, arches, grand staircase - you can hit them all in a couple of days, and i also recommend kodachrome (state park) which is nestled in between zion & bryce i think.