Sunsanee, the character, is suppose to be more evil. She knew exactly what she was doing and she did it all until the final moment of the lakorn. For like 10+ years, she even convinced soriya that she saved her life. all just for her own selfish endeavors. it takes a pretty evil person to be like that from childhood all the way into adulthood.
as for leela, it wasn't like she was raised to be evil. she had true love for kawee which sunsanee only had for herself. and when she realized that it was unrealistic, she did try to move on with someone else. but of course, as fate would have it, her new love gets killed by someone who is in tie with kawee! as for marrying kawee's father, there was potential for her to move on, even if her intentions were not completely inspired by love...and especially if his father did not have a heart condition. but it just seemed as though everything which was close to a dream coming true was somehow always destroyed by kawee's existence.
moreover, she was obviously in denial. she was convinced that she was not hurting anyone. keeping kawee away was killing many birds with one stone. to her, everyone was being blinded by kawee's charades...which was what he was doing for more than half of the lakorn anyways. and in her head, she would be "protecting" narin, herself (as in sparing her own feelings), her family, AND even get revenge.
so, unlike sunsanee, leela had a heart. even though leela's heart misguided her and made narin suffer, she didnt see it that way and she ultimately came back. sunsanee never did.
the reason why everyone think leela is more evil is because the role was portrayed at a much higher level than the role of sunsanee. i like rinlanee, but she didn't do as great of a job as nampeung who was phenomenal at portraying leela.
