A more interesting Q is who would have the better Greatest Hits out of Bey and RiRi. 18 tracks a piece, it's a tough call:

Beyonce:
Crazy In Love
Baby Boy
Me Myself and I
Naughty Girl
Check On It
De Ja Vu
Irreplaceable
Ring The Alarm
Beautiful Liar
Listen
Single Ladies
If I Were A Boy
Halo
Sweet Dreams
Diva
Run The World
Love On Top
Best Thing I Never Had

Rihanna:
Pon De Replay
SOS
Unfaithful
Umbrella
Don’t Stop The Music
Disturbia
Take A Bow
Russian Roulette
Rude Boy
Only Girl
What’s My name
S and M
Cheers
Man Down
We Found Love
Where Have You Been
Diamonds
Stay