Hope: nothing in her entire (often self-righteous, stupid, immature) life comes even remotely close.
Steffy: I guess an argument could be made that Cousin Killer is in the ballpark. But killing Aly was self-defense and she never actually succeeded in killing Ivy. Maaaaybe her clear intention to pass what she thought might be Bill's baby off as Liam's but that didn't happen (as far as we know). So no. For all her despicable behavior, she's never done anything as bad as Flo.