Current Pitt student. If you're certain you want to live in Seattle or at least match in-region for residency, going to UW is the better option. You'll always have the hometown connection and can certainly match there or anywhere else coming from a place like Pitt, but you will always have a significantly better chance of matching your home program versus anywhere else.
Pitt is definitely the smallest city of the three, but I'd hardly call it a small city. It's a great town overall.
The difference in educational opportunities between the programs, realistically, is negligible. What you choose to do with your time in medical school is what will make the difference.
Regarding vibes on interview day, honestly some places just have weird medical students who volunteer to interview and it's not an accurate representation of the student body. Moreover, the composition of your class may be entirely different, and you'll likely find "your people" in just about any class.
Future aspirations + cheaper -> I think your answer is UW. If you want to get out of Dodge for a little while, full send to Pitt. Good luck.