Welp, first I'd distinguish between illustrators--artists who create images to support written narrative--and comic artists who draw comics.

I'll try to link to specific examples this weekend, but my opinion of the best storytellers in comics include:

Alex Toth
Will Eisner
Harvey Kurtzman
Jack Kirby
Steve Ditko
Johnny Craig
Spain Rodriguez
Carmine Infantino
Jaimie Hernandez

Definitely Toth, the EC crowd, Eisner and Kurtzman, Los Bros, Ditko, Infantino, Kubert, Buscema, Steve Rude, Tim Truman, Howard Chaykin, Walt Simonson, Simon and Kirby, Barks, Warren Kremer, Don Newton, Doug Wildey, Pete Morisi, Gen Colan, John Romita.....

Storytelling is about the mechanics of advancing the plot and building the characters. The masters made the quiet moments as significant as the action. Kirby is noted for his action; but, if you look at a lot of his material, especially when he was really cooking, even the small moments draw you in.

Illustration is about capturing that key moment or scene. Guys like Raymond and Foster were illustrators of the old tradition, while Caniff and Crane were storytellers, first and foremost. Those were the guys who set the tone for the Golden Age. A lot of later artists added a design element, like Neal Adams and Howard Chaykin. That is also there in Winsor McCay's Little Nemo.

The really good ones includes folks many here have voiced dislike over or consider them to be blah:
Heck, Tuska, Robbins, Trimpe, Infantino, Brown, Sal Buscema, Mooney, Delbo, Dillin, Sekowsky, Springer, Boring, Swan, Andru, Kupperburg and other such contemporaries of their time. They knew how to tell and sell a story which is why they were considered the go to guys by the publishers. They may not be the most spectacular or stunning stylizing around but their art was always in service of the story line. You knew whenever you saw these guys drawing an issue you were guaranteed an entertaining and compelling read and you would never get lost trying to follow the story or action. 

Well I have to give it to the Marvel Silver Age guys who really had to tell the story. The DC guys worked from more formal scripts.

So first and foremost, Kirby. But kudos to Ditko, Romita, Colan, both Buscemas (I loved Sal's smooth storytelling), Kane.
And I would add Steranko, Smith and Adams into the mix.

The DC artists still did the majority of the storytelling - they chose the size of the panels, importance of the story beats, they picked the camera angels, created the mood, defined character through body language.... Basically they did everything that a movie director and cinematographers (combined!) did, plus a lot of the acting.

They just did a little less than the Marvel guys. But the story is always less important than the telling.

I'd call Steranko and Adams creative designers rather than good storytellers. Adams especially made drawing choices that look cool but don't seem to benefit the story at all. Or, to put it another way, he invented modern-style superhero storytelling!

I don't think anyone has ever topped John Stanley in terms of smooth and effective storytelling.

I'd also put John Byrne and Jim Aparo high on my list of great storytellers. I believe Byrne's stuff was used at the Kubert school as an example of great stroytelling.

IMO a good storyteller is an artist that you can understand the story without any captions or dialog. I remember when I did my reviews on Kubert's Tarzan I commented on this every issue. His art could tell the story without any other descriptions.