Well, my five year old daughter wanted recently desperately ABBAs Greatest Hits, so i listend to it too...
My favourite 5
5. Mamma Mia
4. Voulez Vous
3. SOS
2. Fernando
1. Gimme! Gimme! Gimme!
...but to be honest, (just like my daughter), I like all of them (for example Take a Chance on Me is just such a great song), and back in the 80s when it was released for the first time the Rolling Stone Magazine summed it up for me...:
"...there are more infectious melodies, grabby hooks, and danceable drum beats on one side of this two-disc set than in most artists' entire catalogs...
Amen...
(and yes, i am old)