I have used Northseattle Transmission several times over the last twenty years, and have never been disappointed. Their customer service is beyond fabulous. I've had Hamilton do complete transmission rebuilds on three of my cars. Two of those three were classics.
I'm in the auto business and visit a variety of different shops throughout the week, so I can tell a good one when I see it. The work I have had done at Northseattle is expensive, but I consider it a good value, otherwise I wouldn't continue to bring them my business. They are totally honest, and you don't have to worry about getting ripped off.
On the last job, I went first to a shop near my home, but I wanted to get a second opinion from Hamilton. He ended up undercutting the first quote by $500, so it's worth it for me to make the special trip. They will back up their warranties 100, too. I had one car for probably eight years after a transmission rebuild, and when there was a problem he towed it in and took care of everything.