The line which is best is the line which allows you to put the most power down on the exit and gain the highest amount of MPH at the exit of the corner. This does not mean having the straightest exit possible, because to have a straight exit you must make a very tight turn, and this costs MPH.
The apex point, the line through the corner, the exit point, and the turn-in point all depend on how the car exits the corner. For the proper exit of any given corner, the car needs to be free. You know the car is free when the steering unwinds smoothly, the throttle is applied smoothly, and the car does not want to push straight off the track, but also does not feel "untroubled" by the exit of the corner. The sensation is "am I going off the track?" not "I am going off the track!" nor "I'm definitely not going off the track".
The fact is the truth of this is between the two lines. The red line pinches the exit too much, requiring you to add more wheel past the apex since the entry is so tame and straight. This will slow you down tremendously. However, the blue line is, quite frankly, a rain line, with an over-exaggerated exit that avoids the rubber buildup.
The ideal line is directly inbetween the two.