@1
"is there ever a good reason to choose a bishop instead?"
++ Yes, but it is very rare. The good reason is the same as for a rook: avoid stalemate. Here is an example:
https://www.chessgames.com/perl/chessgame?gid=1253800
Under-promotion to a knight?
Sort:
In this position (I was playing black) if I had promoted to a queen I would have gotten checkmated on the next move. I promoted to a knight and got the win--the only time I have under-promoted.