Benton. The Tri-Cities are the worst.
At least Benton's populated and has actual stores you can shop at if you live in Walla Walla. I've seen some great sights on the Columbia around there. On the other hand, I can't think of a single redeeming quality about Lincoln County, WA. Wahkiakum County is super pointless, too.
Yeah, but I didn't feel like calling any of the empty counties "the worst" just because there's nothing in them. Garfield County is empty and pointless, but I bear no antipathy towards it.
I don't even dislike Eastern Washington that much. It sucks compared to Western Washington, but Spokane is an alright city, Leavenworth is cool, Pullman is fun, Walla Walla is quaint, and every time I drive through Yakima I at least get to see a bunch of cool military vehicles. Tri Cities is a nuclear plant and the blandest patch of suburbia.