X2 on the Benchmark series of western states atlases. They have excellent detail for all public lands, secondary roads and gravel roads if you like to sitesee.
We only travel interstates when absolutely necessary - which isn't much. We love the secondary roads for travel with our 40' motorhome. We've never encountered the need for the 'trucker's atlas' when driving in the west and have never had issues on the secondary roads we travel.
OP: If you're planning a special western trip and staying in one state fairly long, it would be worthwhile getting the Benchmark atlas for that state. As full-timers, we had one for each state. We have a Garman also, along with DeLorme's mapping program on the computer but we use the Benchmark as our very first planning tool for detail.
Perhaps if only driving east of the Mississippi, the trucker's atlas might be helpful.