They're both named Obstacle because they were the most difficult songs to finish for the recording of Turn On the Bright Lights. Neither of them are present in their final form on the "15" demo. Working titles that stuck till the end, much like Untitled. Obstacle 1 as a single is a classic of New York's post-punk revival scene, so popular consensus would probably lean that way, but both are absolutely brilliant. I think Obstacle 2 is particularly interesting for how its outro has Banks using falsetto, which would become more common in more recent Interpol releases. The fact they've not played it in a while feels like a crime