Kind of depends on your interests!
I know people who come to the west and spend the whole time in cities: LA, Las Vegas, SF, and so forth; all the rest is just wasted time in between cities. Other people find nothing of interest in cities and spend their time out of doors, of which there is richness in the west.
Similarly, among those who come west for the out of doors, there are those who prefer to stick to the high mountains and forests, and those who want to see the landscapes, flora and fauna of the great basin.
And there are those who are interested in the rich and ancient cultural history of the west.
Whatever you're interested in, there is enough here to occupy you for a lifetime or two.
My recommendation is to pick a rather smaller area of the west to explore (it's way too big!) and research what interests you in that smaller area.
:)
Lynn