herky
YEAH JEETS!!!!!!111
If I had to pick I'd say when the Monday Night Wars were going strong. Both companies stepped their game up to compete: you had the NWO, Goldberg, and the cruiserweights plus Rock, Austin, HHH all in their prime.
I also think that this is why they refuse to acknowledge the presence of TNA. Things during the MNW could have gone differently, and they almost did.