I am no expert but here are my thoughts:
Speed-wise, I don't think there is any difference between either method. However, it seems to me that the first method will allow only 2 open connections at a time. The second method will allow more than 2 connections. The more connections vsftpd has to deal with, the slower it could become.
But if you are comparing one single connection on either the first method or the second method, then performance should be equal.