If I could only use three social tools I would probably use Buffer, Canva, and the Twitter App (boring I know).
Buffer: To me Buffer is a vital part of my social presence because it helps me schedule out my posts simply and get a quick view of the results of each post I share.
Canva: I love including images in my social updates. They are a great way to engage my audience in a different way and Canva is my favorite tool for creating images and editing photos.
Twitter App: I struggle to find a social listening and engagement tool that meets my needs for a price that fits my client base. This has lead my to use Twitters official iphone app to monitor engagement and engage with friends online.