Vriska killed thousands of people to feed her Lusus so she wouldn't be killed, Terezi killed millions of people just so she could live out her justice fantasies. Terezi is also way more minipulative, literally stabbed Vriska in the back, and went in to self hatrid, Vriska is really trying to redeem herself.

That depends on how you define cruel. Vriska's actions speak louder than her words in my opinion. Yes, she did try to redeem herself, but she was cruel. Forcing Tavros to "fly" is a cruel way of trying to boost his self-confidence.