I am in no position to give an objective answer.
With neek2o, we are trying to create a user friendly environment that can function aside cios and usb loaders.
Therefore, we are trying to create an usb only setup, and we moved the nand folders from the root of the usb disk to any subfolder.
And, not to forget, we let it play your backup games in wbfs format so that you don't need to convert them all.
Furtheron, it will allow in future to use homebrew programs with usb access.
Your question was sneek or uneek. sneek is usually a little slower as sd card access is slower. Also, why would you place your 512MB nand on a sd card if you have a 100+gig harddisk.
Sneek has the advantage that homebrew could access the harddisk. With sneek+di, this option is gone again. In such case, even sd access is a problem since sneek uses it for it's nand.
di uses the usb disk for it's games, so none is available anymore.
Sneek has the option to run dml and play gamecube games from the front sd card. This is not possible with uneek for the moment.
Crediar restarted his work on sneek and uneek. Let's say we are looking over his shoulder to add the goodies to neek2o as well.