By comparing the sizes of the windows, doors, registrations, and American flags of the two aircraft; not to mention the fact that the 767 is much larger than a 737, I believe that the 737 is closest.
And if that doesn't convince you, I searched the Airliners.net forums and found the exact same post as this one. One of the members contacted the photographer, and here's the response:
[ QUOTE ]
Thank you for your interst in the photo. I had no idea that it would come to this, but I truly do appreciate the interest. The answer to the question is the 737. Just by looking at the photo, the best evidence I could come up with would be the relative size of the main passenger doors or even the relative size of a 767 vs a 737. And just to clear up any controversy, I do actually have a photo showing the 737 in front.
Thanks again,
-Stephen Rubke
[/ QUOTE ]
Case closed.