Ring Ring: 5, best song Ring Ring
Waterloo: 6, Waterloo
ABBA: 8, S.O.S.
Arrival: C, Knowing Me Knowing You
The Album: D, Eagle
Voulez-Vous: 7, Voulez-Vous or Does Your Mother Know
Live at Wembley Arena: 9, Gimme! Gimme! Gimme! (A Man After Midnight)
Super Trouper: A, The Winner Takes It All or Our Last Summer
The Visitors: B, The Visitors

Also, I would not neglect:
Chess (Benny Andersson, Björn Ulvaeus & Tim Rice): D, Opening Ceremony, Nobody's Side or Anthem