Is it even possible to go left as you emerge from customs? I don't remember anything in that direction that was available to the public. If one assumes the turn right is the only path then the colectivo window is the last window on the left. I always buy my tickets in pesos which is one reason I make sure to leave the island with plenty of pesos. I don't want to be under pressure to get to an ATM or cambio soon after arriving. I have 1500 pesos in my desk right now and my gf probably has some in her purse. A change in exchange rate could be in my disfavor but that too is lost in the noise.
The two windows are across from one another, last booths.
There is stuff down to the left but you have to turn left into a narrow hall and wind thru there - Federal Police office, the customs office and Immigration office.