i personally like big sand mountain utah its has the second biggest sand hill in the united states i think, im preatty sure that the dunes in idaho are like 50 ft higher but in utah theres a little of everything there some trails, some bowls and just cruisin around dunes, huge a$$ hill, and if you go behind big sand mountain there is some rugged shit that will make you shit your self being your first dune trip im sure youll have fun anywhere i would just find the closest one to you so you get more riding time just my opinon