I got certified at Underwater Sports about 4 years ago, and both the instructors and the people who work in the show are great. During the winter time, they often have a buy one get one free deal on certification classes because not a lot of people want to get wet in the chilly months, but its definitely worth it. It was actually warmer in the water than it was outside when we took our final dives at Alki.
The staff is very well educated, and has tons of dives under their belts. They are extremely patient with the students that are having a harder time...Not to mention that I have never met a diver I didn't like!