Ultron vs Doctor Doom vs Magneto vs Loki

4 of Marvels best villains in fight. Which 1 would win?

(Assuming he's got some sort of defense against Magneto's powers, similar to Dr. Doom)

Ultron.

Hell, Magneto's so damn weak now I wouldn't be surprised if a case could be made in Ultron's favor even if Magneto's powers do affect him.

Loki and Doom's best chance against him would be to BFR, as he's got them beat on raw power significantly as well.

Which version of Ultron?

Probably Doom anyways.

Depends on the stipulations

@kgb725: Unless stated otherwise, the stipulations are usually assumed as a random encounter, in character, most recent versions, etc.