Well, yes, I agree that the Daleks are probably the Doctors greatest enemy, but the biggest villain is the Master.

There's a subtle difference between enemies and villains. Check the dictionary. Enemies are actively hostile opponents, so the Daleks fit that bill perfectly. Villains are wicked rascals, and that describes the Master perfectly. He even looks like he's come straight from a Pantomime !

But perhaps the biggest villain is the person who decreed that Daleks could now fly. The Daleks menace originally came from the way they slowly trundled around corridors and there was absolutely no escape from those indestructible metal monsters.

The Daleks shape is of course ideal for trundling around corridors. It just doesn't work when they fly. They have all the aerodynamic properties of a Pineapple.

Now that Daleks can fly their menace has gone. We're not as easily frightened by something that simply doesn't look right. Daleks have become the Space Invaders in the arcade game and nobodys frightened by that because we know they can easily be shot down.