I used Seattle City Car a few times before switching to Uber. I thought they were reliable and competitively priced. http://www.seattlecitycar.com/
Regarding Uber, I travel a lot and always use UberX to go to the airport (usually $21). I have never had to wait more than 10 minutes for a pickup and find it be very reliable. Unfortunately UberX cannot pick up AT the airport, so I use a taxi to get home (usually $40+).