Okay, so this is my trinity. I have been trying to decide on it for a long ass time now, because my taste is always changing.
#1:
Blackout: I am obsessed with this era of Britney, so between that mysterious, interesting era and the quality, sleazy BOPS it had. I live for this album and it will always be #1 for me.
#2:
Glory: Tbh this is her best album, but I live for the Blackout era so much it edges Glory out for the #1 spot. Slumber Party is perhaps my favorite song of her entire discography. I hate the cover, and the visuals in general are pretty atrocious, but the album is >>>>>>>
#3:
Circus: I LOVE the Circus era sooo much

Even if the album was atrocious I'd love it just bc of the era. Phonography, Kill The Lights, and Circus are THOSE bops and go all the way off. Even though in general is lacks personality the personality Glory serves, it just feels sooo Britney.
Femme Fatale is in 4th place, then In The Zone, then Oops! I Did It Again, then Britney Jean, and lastly Baby One More Time.