Are Bishops more valuable than Knights?
There's a lot that can be said on this topic, but here are some of the factors that enter into my decision making process:


I have a personal preference for Bishops over Knights. This has nothing to do with their inherent value, but is simply because I tend to utilize Bishops better. It's worth considering whether you have a penchant for one over the other, because your personal play style may determine which is more valuable for you.
In general, Knights are better early in the game and Bishops are better late in the game. This is because, in the early game pawns tend to obstruct Bishops, while Knights can move more freely. 
There can also be a difference in value between Bishops (the so-called Good Bishop and Bad Bishop). If most of your pawns are on black squares, your "white" Bishop (the one on white squares) has greater freedom of movement (Good Bishop), while your "black" Bishop's movement will be hindered by your pawns (Bad Bishop). Your Good Bishop probably has a higher value than your Bad Bishop at that point. A common tactic is to trade your Bad Bishop for your opponent's Good Bishop. This can create a slight advantage. You might also trade your Bad Bishop for one of your opponent's Knights.
Two Bishops is generally better than two Knights or one of each. Engineering exchanges that result in you keeping two Bishops and leaving your opponent with two Knights or one of each, may result in a small advantage for you. It's debatable whether two Knights are better than a Knight and Bishop. I tend to think so, but it's very situational. 


Obviously, these are generalizations that may not always apply. Chess is a complex game and the situation on the board dictates what makes the most sense, but they are reasonable rules-of-thumb and worth keeping in mind. The real answer depends on your strategy, your opponent's strategy, and the current state of the board. That is what really determines the relative value of the pieces at that moment.