Seattle might be a good choice.

I live in Columbus, Ohio. One thing Columbus is known for: The average demographic of Columbus closely resembles the average demographic of the overall US.

For that reason, many companies use Columbus as a "test market" for new products. For example, did you know that McDonald's experimented with selling pizza? Apparently, it wasn't a huge success in the trials.

However, as Robert Waltz points out, both Seattle and Columbus are in the top 20 of largest US cities by population.

There's a list here: https://www.moving.com/tips/the-top-10-largest-us-cities-by-population/

Cheers,
Michelle