The problem with choosing a regular subject is that I can't tell which of the above is the sharper because I don't know what part you are specifically focusing upon. 2 looks to be the sharpest overall of the subject, but slight lean in the subject or you focusing on something other than the big circly bit at the top means that I might be making a wrong assumption as to the focus.
Many people like to do tests because "they know they should do them" but they also find test charts boring to shoot - so they pick something more interesting. A flower outside is highly susceptible to wind motion and not an ideal test for fine tuning focus accuracy. Indoors - good light and flash - with a test chart (dull as anything) at the 45degree angle to the camera body. Boring - dull - tedious and not the kind of shots you'll be doing anything with save testing - but it works. It's methodical - it removes the most chances for user and environmental error and its repeatable to check after. Note make sure you have good lighting - slight miss focusing when testing in dim conditions isn't going to show a natural camera inaccuracy with the focus calibration, but might just be showing you that you pushed it a bit too far in dull conditions.
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