From BOMT: You Drive Me Crazy
From Oops: Either Can't Get no Satisfaction or Oops (Around the same ammount)
From Britney: Boys
From ITZ: Me Against The Music The Rishi Rich Remix
From My Prerogative : Do Something
From Blackout: Get Naked
From Circus: If U Seek Amy
From FF: I wanna Go
From BJ: Alien

Rita Ora- ORA: Radioactive
Olly Murs- Right place to right time: Troublemaker
Radioactive too by Imagine Dragons

Baby One More Time: I Will Be There with 708 plays

Oops: When Your Eyes Say It with 568 plays

Britney: Overprotected with 2890 plays

In The Zone: Showdown with 1008 plays

Blackout: Perfect Lover with 1237 plays

Shitcus: Blur with 964 plays

Femme Fatale: He About To Lose Me with 2001 plays

Britney Jean: Work Bitch with 304 plays

Hard to say for Taylor, cause I just recently joined last.fm, but I guess it would be:

Taylor Swift - Tim McGraw
Fearless - Love Story
Fearless (Platinum Edition) - Forever and Always (Piano Version)
Speak Now - Enchanted
Red - Holy Ground

From Lorde's is

The Love Club - Bravado
Pure Heroine - Royals



EDIT:
My most listened song ever is Royals and only today cracked 100 listens
How can anyone listen to a song 1000+ times?

Madonna - Borderline
Like A Virgin - Stay
True Blue - Open Your Heart
Like A Prayer - Like A Prayer
I'm Breathless - I'm Going Bananas
Erotica - Erotica
Bedtime Stories - Take A Bow
Ray of Light - Drowned World/Substitute For Love
Music - Impressive Instant
American Life - Hollywood
Confessions On A Dance Floor - Hung Up
Hard Candy - Devil Wouldn't Recognize You
MDNA - Girl Gone Wild

Gaga
TF: Paparazzi
TFM: Telephone
BTW: Heavy Metal Lover
AP: Venus

Kanye
CD: Get "Em High
LR: Crack Music
G:Good Morning
808s:Say You Will
MBDTF: Power
Yeezus: Blood on the Leaves

I listen to those songs at least once every other day lol.

Also, both songs have been out for a long time.

Rosso Relativo: Imbranato (290)
Centoundici: Non Me Lo So Spiegare (489)
Nessuno È Solo: Ed Ero Contentissimo (2023)
Alla Mia Età: Il Regalo Più Grande (1441)
L'Amore È Una Cosa Semplice: La Differenza Tra Me E Te (4114)

Thankful: Just Missed The Train - 295 plays
Breakaway: Since U Been Gone - 346 plays
My December: Don't Waste Your Time - 409 plays
All I Ever Wanted: My Life Would Suck Without You - 217 plays
Stronger: Stronger (What Doesn't Kill You) - 964 plays
Greatest Hits Chapter One: Catch My Breath - 3237 plays
Wrapped In Red: Winter Dreams - 908 plays

I joined to lastfm a week ago, so they don't have many plays.

Florence and the machine:

Lungs: Rabbit heart - 24
Ceremonial: Shake it out - 14

From my iTunes

DIL- CIL
B'Day- Upgrade U
IASF- Single Ladies
4- Countdown
BEYONCÉ- Partition & Drunk In Love tied

Countdown has the most plays (3044)

Lady Gaga:
-The Fame: Poker Face
-The Fame Monster: Monster
-Born This Way: Judas
-Artpop: Applause

Katy Perry:
-Teenage Dream: Dressin' Up
-Prism: Dark Horse

Ke$ha:
-Animal: Take It Off
-Cannibal: Blow
-Warrior: Supernatural

Rihanna:
-Loud: S&M
-Talk That Talk: Where Have You Been
-Unapologetic: Right Now

Britney Spears:
-Blackout: Break The Ice
-Femme Fatale: Hold It Against Me
-Britney Jean: Work Bitch

Selena Gomez:
-Stars Dance: Save The Day

Stan for the best song ever

Demi

Don't Forget: La La Land
Here We Go Again: World Of Chances
Unbroken: Give Your Heart A Break
DEMI: Neon Lights

Little Mix

DNA: Change Your Life
Salute: Salute

Imagine Dragons

Night Visions: Demons

Gaga
The Fame: Poker Face
The Fame Monster: Telephone
Born This Way: Marry the Night
ARTPOP: Applause

Ashley
Headstrong: He Said She Said
Guilty Pleasure: Crank it Up

Adam
For Your Entertainment: Music Again / If I Had You
Trespassing: Never Close Our Eyes

Nelly
Whoa, Nelly: I'm like a Bird
Folklore: Try
Loose: Say it Right
Mi Plan: Manos al Aire
The Spirit Indestructible: Big Hoops (Bigger the Better)