I have been flying Alaska Airlines for the past 10 years, hands down the best domestic North American airline. Delta is close behind, United, American, SouthWest have nothing on AS in my opinion. Most recently changed from home airport in Milwaukee to O'Hare due to proximity and number of flights available. MKE and AS are more recent, great flights on E175 (2x2) aircraft. MKE-SEA is year round once a day, PDX added last year as seasonal only.
This past week ORD-SEA aboard 737-9 both ways in economy. Outbound I opted for $49 extra to sit in E+, very comfortable and spacious. The 6AM flight on Monday was half full, entire rows were empty. Overheard a FA say this was the emptiest flight she'd seen from ORD but it's also in that holiday break period. Normally E+ includes a free alcoholic beverage, at 6AM thought not a wise idea. The new overhead bins allow for greater storage but still no issue due to capacity on this flight. Return flight on redeye was also half capacity. I had booked E+ two days prior but day of flight I was unable to check-in. I later learned the 737-9 on this route did not have E+ seating except emergency exit rows. Not a major issue, but would have been nice to know ahead of time despite being allowed to book E+ on seatmap 24 hours prior.
Do Not book a middle seat on the 737-9. The middle seat has the IFE box at it's feet, removing some space. Aisle seat unfortunately loses a small portion of foot space to this as well, but IMO not a major issue.
Customer service at Alaska Airlines has always been a strong point. Baggage guaranteed within 20 minutes or free miles offered, just another reason why I love Alaska. This is not a budget airline, but it does pale in size compared to the big 3. I don't mind the Q400's when visiting family in Lewiston-Clarkston or Pasco, but maybe that's the plane enthusiast in me too. Would recommend Alaska Airlines particularly if your travels involve the west coast and smaller markets like Walla Walla, Spokane, Boise, etc..