I must admit I've never had a favourite chart of choice, nor can I immediately recall a data presentation either bad or good enough to stick in my memory. But I have tried out one of the data visualisation tools mentioned in Georgina's post. I went for easel.ly, the one that had been used by the other participants, following their praise for its ease of use. It took me a certain amount of trial and error to use it, especially as I didn't see a 'Help' page. However, I hope you agree I have succeeded in making a Venn diagram of data from my blog post of January 2011, on poetry competitions.
The data concerns my poetic output from 1977 to 2011, as recorded in the card index I've kept since 1994. Of a total 218 indexed poems, I counted 95 that had been specially written for competitions, 67 that had been published, and 25 that had been both written for competitions and published. Making the Venn diagram required some revisiting of 'O'-level maths, to determine whether the radii of the smaller circles should measure against the large circle in the ratios 95/218 and 67/218, or in ratios of the squares of 95/218 and 67/218, or in the ratios of the square roots of 95/218 and 67/218. But I think I got there.
I have not used Microsoft Excel's SmartArt facility, but I suppose I had better try it some day, if I'm going to make a habit of Venn diagrams.