Who's more *overtly* scary when pissed off? Superman, because the nature of his powers/schtick is more blatant.
Who's more *subtley* scary when pissed off? The Doctor, hands down, as were he to really let loose with what he is potentially capable of (as he has been gradually doing over the past couple of seasons or so, which is why he is slowly becoming mentally unstable) not only could he redefine (literally) the meaning of hell-on-earth (or anywhere else, for that matter), he could arrange to have reality be so utterly different from what is was that those he targets with his wrath would not only suffer in ways Kal could not even begin to imagine, he could make it so those affected *thank him* for it, believing him a friend, only to have "the great reveal" shatter that perception... only to have the whole thing repeat all over again... and again... and again... and again... and...
__________________ Why am I here commenting on this crap?
I mean, he wouldn't be scary in the whole 'RAWR BREAK YOU DOWN WITH MY FISTS OF RAGE' that a PO'd Supes would be, but the Doctor would be far more brutal with his punishments if his back was against the wall.
For one, the combination of the technology he has access to and his intellect makes him incredibly dangerous, and the fact that if he wanted you to suffer you would.
A good example would be in the episode where he confines the members of the family of blood to immortality, trapping one in a mirror, time freezing one and turning him into a scarecrow, etc.
Superman doesn't kill. And while the Doctor is against killing, he has killed. And he could do worse than kill...I'm not really sure Kal is capable of anything worse, even pissed off.
In retrospect, the Doctor being morally against killing never stopped him from effectively commiting a double genocide and killing more people than most supervillains in one go.
Again no one's argued that Superman isn't more intimidating in a direct sense but Dr. Who is certainly more intimidating in the grand scheme of things. It's like the question of who's scarier: Joker or Lex Luthor? Of course Joker is more directly scary but the worst he'll do is kill you (okay maybe worse than that but most likely he'll only kill you). Piss Luthor off though and before being killed you'll find your entire family in poverty, your little sister and mother forced into prostitution, your father committed to an insane asylum and your girlfriend knoicked up by, you guessed it: Lex Luthor. Only after all this sinks in will Luthor kill you.