Crono is more interesting than Sephiroth, and he took out Lavos, while Sephiroth was taken out by Cloud, a somewhat less powerful person.
Therefore, Crono wins on both counts.
I should, however, point out that this interesting bit is relative...neither Sephioroth nor Crono are fleshed-out fully human characters...they're both more like one-dimensional attempts. Crono, however, was meant that way, so he gets a bonus, versus Sephiroth, who just keeled over and collapsed.