Hawkeye since he went on a killing spree. Granted, he didn't kill good people but still.
Wanda is in second because she essentially held innocents captive in her created reality but she didn't intentionally set out to harm anyone. I felt the most sorry for Wanda because it felt like everyone forgot about her. At least Natasha was actively trying to find Clint and help him when he went rogue.
Thor only really harmed himself so I wouldn't qualify him in the same ballpark, although it's hard to tell how many lives could have been saved had he been actively doing his job as protector of the nine realms during his five year binge.