Your bow arm should be in the position that creates the least amount of tension in that bow arm. Typically this is done in a straight position, however don't confuse the term straight with "locked" or hyperextended. Every persons body type is different though, so this may vary from person to person.

I personally shoot with a straight bow arm, with the inside of my elbow at a 45 degree angle to the ground, and my front bow arm shoulder low and bottomed out. This is where I develop the least amount of tension in my shot, and where I am most consistent.