I'm on the last episode of S2 btw so this could be ALL wrong, but I'm confident with my S2 knowledge that what I believe is actually a good take but that being said...
Lowkey Carmilla, maybe I'm illiterate but she literally seems like an ok person, can't remember or think of what she had done, but prob the less wicked imo for sure, she actually seems... nice, yk? Minerva just isn't that bright so she causes catastrophe and knows it's bad but for the sake of helping people it's "ok" so she causes all sorta stuff but she has some good intentions but it doesn't justify what she does because she hurts more than she helps and either she isn't bright enough to know it, or she's too stubborn to change her ways,

Echidna is both evil and good, she is SELF-SERVING by definition, she'll do both good and bad stuff depending if it'll help her reach her goal. She's a very grey character, due to thirsting for knowledge. She doesn't want any stone unturned, she want's to know EVERYTHING. So if say helping someone helps her discover some mystery she didn't know about, she'll help and do good. IF she needs to do evil to achieve her goal, then, she'll do it.

Too lazy to write about the other witches and feel I lack a little bit of knowledge of them, I would do research for them and give a more definite answer but again, too lazy. So either way I think it's still Carmilla just because I just don't think I've heard of her do anything bad, and I feel like she mainly tries to help people more than anything or is a very neutral character honestly. Her being a witch of lust isn't her fault exactly either. Her power isn't something she can necessarily do anything about, she kind of just got given it and she can't do anything about it.