There's no definitive answer to this question - it depends on the overall design of the shirt and where you want the focus to be. If your shirt has a lot of other graphics or text, you might want to put the logo on the left so it stands out more. Or, if you want the focus to be on the chest area, putting the logo on the right might be a better option. Ultimately, it's up to you and what looks best with your particular design.