domestic · 2h 45m · 1,642 km
Seattle to Denver
4 airlines · 4 aircraft ranked
In economy, Alaska's Main Cabin (737-900ER) edges out the field with a 4.4/10.In first class, Alaska's First Class (737-900ER) edges out the field with a 2.8/10.
Quick pick
Fly Alaska. It scores higher across seat comfort and amenities.
If prices are similar, go with this one.
Fly Alaska. It has 3 more inches of legroom and a wider seat (21" vs 20").
If fares are comparable, this is the better cabin.
Select two airlines to compare head-to-head
Data verified June 2026
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Airlines on this route
Flying with family
- Seatback screens on Alaska, United. Southwest, Frontier: bring your own device.
- Most legroom: Southwest (32"). Least: Frontier (28"). That 4" difference matters with kids.
Route insights
- In economy, Alaska's Main Cabin (737-900ER) edges out the field with a 4.4/10.
- In first class, Alaska's First Class (737-900ER) edges out the field with a 2.8/10.
Frequently asked
Which is better in first: Alaska or United on SEA-DEN?
First Class (Alaska Airlines, 737-900ER) and United First (United Airlines, 737-900ER) score virtually the same in first: 2.8 vs 2.8/10. The biggest gap is seat width — 21"-wide seats vs 20" — but neither carrier pulls ahead overall.
Which is better in economy: Alaska or United on SEA-DEN?
Main Cabin (Alaska Airlines, 737-900ER) and Economy (United Airlines, 737-900ER) score virtually the same in economy: 4.4 vs 4.2/10. The biggest gap is power — AC + USB-C vs USB-C only — but neither carrier pulls ahead overall.
Which is better in economy: Alaska or Southwest on SEA-DEN?
Main Cabin (Alaska Airlines, 737-900ER) edges out Economy (open seating) (Southwest Airlines, 737-800) in economy, scoring 4.4/10 vs 3.9. The deciding factor: a 10" screen vs app_only. Southwest Airlines fights back on legroom.
Which is better in economy: Alaska or Frontier on SEA-DEN?
Main Cabin (Alaska Airlines, 737-900ER) dominates Economy (Frontier Airlines, A320neo) in economy, scoring 4.4/10 vs 2.2. The deciding factor: 31" of pitch vs 28". Frontier Airlines fights back on seat width.
Which is better in economy: United or Southwest on SEA-DEN?
Economy (United Airlines, 737-900ER) edges out Economy (open seating) (Southwest Airlines, 737-800) in economy, scoring 4.2/10 vs 3.9. The deciding factor: AC + USB-C vs USB-A only. Southwest Airlines fights back on legroom and seat width.
Which is better in economy: United or Frontier on SEA-DEN?
Economy (United Airlines, 737-900ER) dominates Economy (Frontier Airlines, A320neo) in economy, scoring 4.2/10 vs 2.2. The deciding factor: a 10" screen vs none. Frontier Airlines fights back on seat width.
Which is better in economy: Southwest or Frontier on SEA-DEN?
Economy (open seating) (Southwest Airlines, 737-800) beats Economy (Frontier Airlines, A320neo) in economy, scoring 3.9/10 vs 2.2. The deciding factor: 32" of pitch vs 28". Frontier Airlines fights back on seat width.
What are the best seats in Alaska First Class on SEA-DEN?
Best: Row 1 for maximum legroom. Window seats in rows 1-2 are quiet and private. Avoid: Row 4 (last row of first) may have limited meal choices due to service order. 41-inch pitch is among the best domestic first class products in the US. No seatback IFE screens; stream to personal devices via Gogo 2Ku Wi-Fi. USB-A and AC outlet under center armrest. Free for T-Mobile customers. Pre-order meals system with limited choices.
What are the best seats in Alaska Main Cabin on SEA-DEN?
Best: Exit row seats (row 15/16) offer extra legroom. Avoid: Last row (34) has limited recline and is near the lavatory. Middle seats throughout. Standard domestic economy with 31-inch pitch. USB-A and AC power at every seat. No seatback screens; entertainment streams to personal devices. Boeing Sky Interior with larger overhead bins. Exit row seats on the 737 offer extra legroom but do not recline. The row immediately before the exit also has limited recline due to clearance requirements.
What are the best seats in United United First on SEA-DEN?
Best: Row 1 has the most legroom as a bulkhead. 1A and 1F offer the most privacy with the wall on one side. Row 2 is the sweet spot between legroom and storage (bulkhead rows lack under-seat storage). Avoid: Row 5 seats 5A/5B do not recline; 5E/5F have roughly half the recline of other First rows. This is the biggest seat trap on the 737-900ER. Signature Interior with Collins Aerospace Pinnacle seats, 13-inch HD seatback touchscreens with Bluetooth audio, USB-A and USB-C at every seat plus AC outlet. Complimentary meal service on flights over 800 miles; snack basket on shorter flights. ViaSat Ka-band WiFi free for MileagePlus members. Starlink awaiting FAA certification for 737-900ER, expected during 2026. Majority of fleet retrofitted to Signature Interior; some older aircraft remain.
What are the best seats in United Economy on SEA-DEN?
Best: Exit row 21 has 38.8 inches of pitch — more than First Class. The 2-seat side rows 20-21 are the best economy seats on the plane. Rows 7-14 are Economy Plus with 33-34-inch pitch. Avoid: Last row (row 33) has severely limited or no recline due to the rear lavatory wall. Rows 32-33 experience galley noise and lavatory traffic. Middle seats (B, E) in any row are the tightest at 30-inch pitch. Signature Interior with 10-inch HD seatback touchscreens and Bluetooth audio. USB-A and USB-C at every seat plus shared AC outlets. ViaSat Ka-band WiFi free for MileagePlus members. 42 Economy Plus seats in rows 7-14 have 33-34-inch pitch; 117 standard Economy seats have 30-inch pitch. Three sub-variants exist (39/42/45 Economy Plus seats); Version 2 with 42 E+ is most common (~84 of ~99 aircraft).
What are the best seats in Southwest Economy (open seating) on SEA-DEN?
Best: 16A and 16F have the most legroom (no seat in front, behind exit row). Row 12 exit row seats also have extra legroom. Avoid: Last row (row 29) is narrower, restricted recline, near galley/lavatory noise. Seats 10A, 11A, 11F lack windows. Single-class cabin. Assigned seating launched Jan 2026. Extra legroom rows at front have ~34 inch pitch. Older 737-800s lack power outlets; newer retrofits have USB-A and USB-C in seatbacks. Streaming entertainment via personal devices only. Exit row seats on the 737 offer extra legroom but do not recline. The row immediately before the exit also has limited recline due to clearance requirements.
What are the best seats in Frontier Economy on SEA-DEN?
Best: Exit row seats for extra legroom without paying for Stretch. Avoid: Last row has no recline and lavatory proximity. All middle seats are uncomfortable at 28-inch pitch. 28-inch pitch ties Spirit for the tightest in the US industry. No wifi, no power outlets, no seatback screens, no streaming entertainment. Tray tables are approximately 50% smaller than standard. All food and beverages are buy-on-board. Individual air nozzles and overhead reading lights are available. Exit row seats on the A320/A321 family offer extra legroom but do not recline. The row immediately before the exit also has limited recline due to clearance requirements.