1. Decentralized
2. Open source code
3. Federates with other services
4. You can easily determine what you’re sharing with whom (Diaspora’s aspects or Google+'s circles)
5. You can easily download all your data if you want to leave
6. Minimal but responsive and attractive UI
7. Accessibility features (i.e. you can add alt text when you post an image)

Diaspora fits most of these, but I think that (early) Google+ had a better UI.