Ultron.

No AM?

Assuming we're talking about the original comic book version of Ultron, he's easily my choice. Probably one of the best Marvel villains ever, right alongside the likes of Thanos and Doctor Doom.

Definitely Ultron. Especially Infinity Ultron

Al-G Rhythm: the most typical AI villain they can think of. Honestly, out of all of them I prefer Ultron.

I like AUTO's design, but I don't like the character as much, mostly because he heartlessly switched off EVE and dumped her down the garbage.