Whirling frenzy is better, and here's why: with regular rage, you gain +2 attack & damage per attack (or +3 damage if two-handed). With whirling frenzy, however, you gain a whole extra attack at your best (normal) attack bonus, plus the extra damage. Offensively speaking, WF is miles better than rage because an extra attack at full BAB is always better than a small bonus to attack on your normal iteration:
+17/+17/+12/+7
verses
+19/+14/+9
With damage being equal, I know which attack progression I'd rather have.