There is no best lens, or best camera for social media. You will see stunning photos online from smartphone cameras to point and shoots to bridge cameras to entry dslrs / mirrorless to high end bodies and glass of all makes and models. It's more about post processing for social media. I shoot raw. I am lazy and just resize to 2000 x 1333 pixels in either LR or PS then convert to jpg in the srgb color space sharpening for social media, but each social media lends itself to different formats and sizes. For example, instagram lends itself to square or vertical crops, facebook is a little more flexible... So, I tend to leave a bit more space around my subject so I can crop / resize as needed.