I'll assume by "main cast," you refer to principal players (in the opening credits) as opposed to recurring characters.  In that case I guess it would be a toss-up between Kenny Ward and Paige Matheson.  Kenny was too one-dimensional, a victim of bad/neglectful writing.  Paige suffered not from bad writing but from over-exposure.  I felt the producers who created her were so enamored of their creation that they insisted on giving her too much screen time.
In recurring players I have several, but narrowed it to Linda Fairgate for the same reason I grew to dislike Paige--overexposure.  They seemed to want to have this newbie make all the established characters look stupid via her scheming. "See how crafty she is? Isn't she clever? Oh, what will she do next??" Oh, give me a break.