If you listen to grand masters (I clearly not am one of them ;), the bishop is better.
Bishop:
- The biggest advantage is his long range.
- Since it is bound to one color, there are some squares that he'll never reach.
- You may checkmate with two bishops.
Knight:
- Jumping. (i.e may move over occupied squares)
- The strange move it does sometimes surprises beginners.
- Going from one square to another one may take several turns.
- It is almost impossible to checkmate with two knights. (Unless the oponent makes a mistake)
Oh yes and anecdoticly it is possible to checkmate with one bishop and one knight.
I personaly like knights for their surpising moves but I have to recon I sometimes had hard finals because of exchanging them to bishops.
So to conclude When you play a game, it is ok to exchange one knight for a bishop but try to keep at least one bishop because of its better capabilities in final for checkmate.
In a chess game what do u think is more important in your game? and why? Personally i enjoy knights.