Bishop or knight?

It depends on the position and how active the piece is because what may appear like an equal exchange could in-fact be much more beneficial to one player such as trading your bad bishop for your opponent's good bishop or a knight guarding your castled pawn wall compared to your opponent's bad bishop. In the endgame when both kings are active a bishop is probably going to be more powerful especially if it's the same colour as a queening square for any passed pawns. I've started to focus a lot more on exchanges and how it benefits my position instead of doing them for no other reason than it gives my opponent doubled pawns. The minor advantage I might get from that will likely soon be lost if it's against a stronger player.

Knights are better early and bishops are better later is a good framework but it comes down to the position which changes with every move.

The simple answer(according to GothamChess) is that in closed positions, the knight is better since it can jump over peices; Whereas in open positions, the bishop is better since it can control more squares on the chess board.

I agree. Once I checkmated with a bishop and a knight, and the knight played the most important role. I'd say middlegame is also knight, so knight overall is best.