Which side of the plane is better?
There is no side that always wins. The better side depends on the direction you fly, the time of day, and what you want to look at. Here is how to work it out in a few seconds.
Start with the direction of flight
Everything follows from your heading. Flying west in the evening puts the sunset ahead of you; flying north in the evening puts it on your left. The sun moves along a predictable arc, so once the heading is known the good side is simple arithmetic.
Left and right always mean your left and right while seated facing forward, which is the same as the aircraft's port and starboard.
Then decide what you actually want to see
A sunset seat and a city-view seat are often on opposite sides. Pick one priority before you choose a seat. Sunsets and sunrises are the most reliable, because sun position can be calculated exactly. City views depend on which runway is in use, which nobody can promise in advance.
Mountains, coastline and islands sit in fixed places, so a route that hugs a shoreline strongly favours the side facing the water.
The quick answer
Enter your flight number or your route on the home page, tick the views that matter to you, and you get a single answer: LEFT or RIGHT, with a confidence rating and short reasons. If the two sides are genuinely close, it says so instead of inventing a winner.