Instagram. Getting your information out there in one image can be hard, especially with the quick-scrolling, short attention span of the average Instagram user. I go for simple graphics with bold titles but include the basic information to make sure it goes with the image if shared.
Facebook. The dimensions for an event page here differs from Instagram but the overall extension of the brand is important. Consistency across all platforms makes your brand easier to recognize and is just plain satisfying to the eye.