Well, what's weird with Britney is that sometimes singles that don't do that well are still well known and love by the gp lol...
I can only talk since blackout because I started following her like 5/6 months before it came out so those albums are the only ones I knew the songs before they became singles.
-Break the ice: I thought it would do great until we had the animated video and I lost all hopes.
-If U Seek Amy: I thought it would be a new iconic song like BOMT but nope, I was so excited for it to be a single...
-Till the world ends: I still think it's weird how it didn't end up being a classic Britney, they still force it on us on every tour lol
-Perfume: It such a beautiful and mature song, a nice follow up to everytime but didn't work I guess
-Slumber Party: everything was perfect, still don't understand why it wasn't a big hit.
Other songs I knew after they were released as singles but was surprise years later that they're not huge hit:
-My prerogative, this is so damn good...
-Toxic, so surprised it didn't went n°1