If you frequently fly solo between Shanghai and Taipei, your best options are to fly from Shanghai Hongqiao Airport (SHA) to Taipei Songshan Airport (TSA). Your airline of choice depends on your desired departure time, but 4pm or later are the best flights due to airline quality and availability.

How I decide on what best is

As I mentioned in my best SHA/PVG-HKG flights post, SHA is always better than PVG. In Taiwan, TSA is also better than TPE.

This means the flight you want is SHA-TSA. Once you've accepted that airport pair is the best, departure time is probably what you will consider as the main factor. Due to the war in the Middle East, airlines are cutting back routes. The afternoon routes below remain for now.

Airline Airline Alliance Departure Aircraft Type Seat Width
Shanghai Airlines SkyTeam 08:15 A330 / B737 17.0" - 18.0"
Air China Star Alliance 12:15 A330-300 18.0"
China Eastern / China Airlines SkyTeam 14:15 A330-300 18.0"
China Airlines / China Eastern Skyteam 16:15 A330-300 18.0"
EVA Air / Air China Star Alliance 19:40 A330-300 18.0"

Why Songshan (TSA) instead of Taoyuan (TPE)

Songshan is a lot quicker to downtown than Narita. If you're familiar with Shanghai, it's a bit like Hongqiao airport (SHA) versus Pudong airport (PVG).

You will save at least 1hr door-to-door time with SHA being 30 mins less travel time than PVG, and 30 mins with TSA being closer to downtown than TPE.

Seats

Other than Shanghai Airlines which offers a wide possibility of seat widths due to multiple aircraft and seat layout possibilities, all the other airlines have 18" seat width.

Airline

Schedule permitting, my suggestion is Eva Air (5-star Skytrax) or China Airlines (4-star) over the other airlines. The rest are 3-star Skytrax airlines which tend to offer food at a quality I wouldn't pay for at a food stand, but I eat just because I'm stuck on a plane, could use some food, and already paid for it.

Takeaway

There are plenty of comfortable seat options available on this route. Even if you encounter the least comfortable Shanghai Airlines option, you just have to endure it for 2hr to 2hr 15mins. Consider buying pre-boarding food if you're not flying on Eva Air or China Airlines.