In graphic novel culture, a series is approached a bit like the old Paul Valery thought, "A poem is never finished; it is only abandoned." Funnily, this is true whether your story is about a boy in a spider suit fighting crime with technical wizardry, or about a rabbit samurai slicing and dicing up the rest of the animal kingdom throughout Japan. Nonetheless, I find myself most drawn to series with a seeming pre-established arc (Brian K. Vaughan, Alan Moore, Neil Gaiman), or series of self-contained stories that form a larger trend (Rick Geary, Frank Miller, James Sturm). And with strips, self-containment, while not always possible, certainly always seems to lead to funnier jokes (Kate Beaton, Alison Bechdel, Nicolas Gurewitch).
One important note: from 87 down, these are series that might be amazing, but I've only read the first volume, or not enough to feel like a proper judge. I decided to include these over series I'm more familiar with, since the promise here feels more rife.