I thought Michael Fassbender's Erik Lensherr/Magneto was the best in First Class. I always loved the theatrics and look of Doctor Doom, but if I had to choose my favourite villain of all time, it would be Magneto. I really loved a lot of elements that went into Magneto in First Class. I liked that he had a mission that wasn't about world domination or mutant rights. He just wanted revenge. Things changed quite a bit when he met Xavier and things really took form for him, as far as the person he'd become in the future at the end of the movie.
When it was revealed that X-Men: First Class was a re-purposed X-Men Origins movie about Magneto, I wasn't surprised one bit.