The coolest (or at least most interesting) version is the 2016 version from the Suicide Squad. Not the greatest adaption, but I really like the unique take on the character that Jared Leto had. I think there was a lot of that version that we never got to see.
The scariest for me is the 1986 version from the Dark Knight Returns. He's not visually grotesque like 2012 or 2019, but his calmness and overall demeanor from the comic and film adaptation definitely terrified me when I first watched it. He's a calculated killer.