...Baby One More Time >> Madonna
Oops! I Did It Again >> Like A Virgin
Britney >> True Blue
Like a Prayer >> In The Zone
Blackout >> Erotica
Circus >> Bedtime Stories
Ray Of Light >> Femme Fatale
Honestly, except Janet Jackson, no other popstars past and present can compare with Madonna's music from the 80's or 90's (partly because music was significantly better during those times) YET Madonna's music has been going downhill since American Life and Britney's Blackout, Circus and Femme Fatale are better than Confessions, Hard Candy & MDNA.
Madonna's earliest albums haven't aged well at all, her most recent albums are completely uninspired, and there's tons of filler to be found across the majority of her discography.
Britney, on the other hand, regardless of whether she's 16 or 30, lipsyncing or singing live, a robot, shaving her head, doing drugs, etc. has always slayed us with completely flawless, next-level pop music and albums that have little to no filler.