Ok here's my reasoning and I know some of you will think I am crazy. Magneto copied Dr. Polaris. Thanos copied Metron and Darkseid. To my knowledge, Dr. Doom is more original than Magneto and Thanos so I like Dr. Doom the most out of the three.
Magneto more original and was very good written in the movies. Plus the bat scene and First class scene are still memorable and this comes from a DC Fan, I own X-Men movies and comics so there might be a reason?