This is hard, but..
OFF: Dip It Low
SAVE: Slave 4 U
I'm a Britney FAN, not stan.. but that's not the reason why I voted 'Dip It Low' off.
To be honest, if 'Crazy In Love' wasn't immune, I would probably be voting that off, or 'Dip It Low', then I'd choose whichever one I didn't choose, then 'Toxic', then 'Dirrty'. But TBH, Slave 4 U wins if it's a sexy video competition. Just following what the title says!