Do some opening lines favor white and others black? Or are they optimized to maintain a neutral position? To answer this question I selected 190 commonly played opening lines (out of thousands) from the "opening theory" book available online at wikibooks and played each one of them on engines in analysis mode and recorded the value of white's position at the end of each line. The data are shown in a pdf file on freepdfhosting.com that can be viewed or downloaded using the link shown below:
Opening data sorted by move sequence: http://freepdfhosting.com/634a84afbc.pdf
The positional values are computed on a scale in which the material value of a pawn is set to 100 points. At the start of the game, white has a positional advantage of 20 points by virtue of holding the first move. Since white's win percentage is higher than that of black's ceteris paribus, we can assume that a 20 point advantage is meaningful in the game. For the sake of the rest of the analysis we shall assume that an advantage of less than 20 points is not statistically important in terms of game outcome. In particular, we should also note that position value estimates have a variability that indicate a measurement error of plus or minus 5 points.
Accordingly, in the second data sheet I have color coded the data to separate the opening lines in my sample into three distinct groups.
Opening data sorted by position value: http://freepdfhosting.com/b1c3a63855.pdf
In the middle group, in black letters, we have about 130 lines representing 66% of the sample with white's position value in a range range from 0 to 40. Since white started with a positional advantage of 20 and ended with a value somewhere between 0 and 40, white's positional advantage did not change by more than 20 points by virtue of the opening moves. We therefore classify these openings as neutral in the sense that the opening moves did not substantially affect positional advantage.
At the top of the list are about 30 opening lines color coded in red in which the opening moves caused white's positional advantage to decrease by more than 20 points. These lines favor black. If the line is a "defense" then we can consider the defense to be an effective one. If it is an "attack" or a "gambit" by white then we can consider the attack to be ineffective. In any event, black's response has been stronger than white's attack and white has completely lost it's initial first move advantage.
The bottom group, colored in green, contains about 30 opening lines which favor white. In these lines white's positional advantage has increased by more than 20 points by virtue of the opening moves. We can therefore consider white's "attacks" in these lines to be effecive or black's "defense" to be relatively ineffective.
In summary the answer to my question seems to be that mostly (in 2/3 of my sample) opening lines played faithfully do not favor white or black but about 1/3 of the lines favor one side or the other and these are symmetrically distributed. Half of them favor white and the other half favor black.
The first pdf file in which the data are arranged by move sequence also serves as a compact ready reference to 190 commonly played opening lines.
Cha-am Jamal, Thailand