I would have felt that this was not even a close comparison 15-20 years ago, to favor Merion by a long shot.
But now that the golf ball is going much further it seems to tip the scales to make the matchup much closer. Then when you add in the recent renovations to both courses. The renovations are more negative to Merion and more positive to AGC with respect to the member golfer.
BTW, I am very familiar with both golf courses.
If you had to pin me down to answer the question, I'll go with Merion........west