This graph, which was first published at the end of March, was one of the ones that really cut through in the Coronavirus story in Australia, in my opinion. https://www.abc.net.au/news/2020-03-25/coronavirus-covid-19-modelling-stay-home-chart/12084144
There has been a huge amount of data and numbers published throughout this crisis, but I think this one was particularly strong because it compared spread predictions under different levels of compliance with social distancing rules. It illustrated very starkly why we should comply with social distancing as much as possible.
I also like the animation further down that shows how social distancing curbs the spread, and I think that gave good context as to why social distancing works and why it's important to adhere to it. To push this message was very important, because Australians often have a 'she'll be right' attitude, and there was a real push for people to take personal responsibility in the efforts to curb the spread.
In Australia, these messages seem to have cut through, as our transmission rate has stabilised a lot, and there's a general sense that we're winning the battle here (at least at the moment), because rates of transmission have plateaued.