Joe Schuster is, hands down, the greatest Superman artist of all time. Sure, his version of the costume looks a little funky and primitive by today’s standards, but the way he drew the character–big but not like a body builder, and with a tough guy grin on his squinting face–is the standard that all other versions ought to be measured against.
Neal Adams defined the look of the Batman for an entire generation. His drawings managed to express the same level of complexity and emotion as flesh and blood actors, yet they were still firmly in keeping with the comic book tradition. What Frank Miller, Neil Gaiman, and Alan Moore did for the quality of scripting in comics, Neal Adams did for the quality of the artwork.
Speaking of Batman, I’m going to have to throw in Bruce Timm for good measure. He took the visual design of Batman down to its most essential characteristics, and still managed to capture all of the things that make Batman great. He then proceeded to do much the same with just about every other major character (and a boatload of minor ones) in the DCU.
Frank Miller’s Sin City series could be used as a text book on how to appropriately shade magnificent two-tone images. It is astonishing how much detail, atmosphere, and mood he is able to convey through such a simple palette.
Jim Steranko was one of the few guys to wildy experiment with format, long after most of the conventions and cliches of mainstream comics were established. He pushed the medium just about as far as it could go while still being recognized as comics.
But I’d have to say that my all-time favorite comics artist is probably Will Eisner. It’s too easy to point out that most of visual vocabulary of modern comics was invented by him, or that he was one of the first guys to promote comics as legitimate literature. His drawings are downright beautiful. His characters have the emotional realism of Neal Adams and his cityscapes are like Jack Kirby on steroids. To top it off, he was never content to stop experimenting with format. Just look back at the stuff he was doing in the 40s… he was laying groundwork for decades of artists to follow. Way ahead of his time. I cannot think of any other artist who was in the business from the beginning and continues to have the same level of relevance as Eisner does today.