Jyou
That was, of course, until everyone became a DigiDestined. But still, the point remains. In 02, he was even in college while everyone else was still in high school. Though, according to the show, he was studying medicine... which isn't something you can do in college. Which just goes to prove that Toei, or at least Saban, is horribly inaccurate.
In 01, Jyou was not a particularly appealing character. He was perhaps more developed than Sora, but I doubt he had too many fans. Usually a whiney coward, he was just as usually the only voice of reason in the entire group. Koushiro, another pacifying voice, was easier to provoke, and also spent so much time at his laptop that he was willing to go with the flow. Sora, another worrier, realized that the best method was to put in her two cents, but allow the group to do as they desired most of the time, only continuing to protest when she believed that there was exceptional danger. Jyou, though pessimistic, a constant worrier, and none-too-brave when he didn't have to be, was always trying and failing to convince the group to take the safer path.
In 02, his character does not become more complex. If anything, it becomes less well defined, since it clearly changes from its earlier form to something new -- but to what is never shown. As a trade-off, though, he does get a very special place in the DigiDestined: he is quite arguably the sexiest character on the show. Taichi and Yamato declined as they aged, Koushiro lost his initial cuteness, and Takeru didn't improve that much. Jyou, on the other hand, advanced with leaps and bounds. His hair grew out, he switches his old round glasses for much more stylish rectangular ones, and he lost his nervous mannerisms. Although still not easily described as "cute," he did become quite sexy. So much so, in fact, that he can't be beat.
Jyou isn't my favorite character, but he's better than quite a few of them. And I would far rather see him onscreen than, say, Sora. All in all, I think that Jyou is a highly under-appreciated character, and something should be done to promote his virtues into the common awareness -- such a kawaii guy shouldn't be enjoyed by just a few!