Loopback seems to be the most organised way to create your APIs.
There's a command line tool to get you started off with your models and relationships. You can create public/private APIs to access these models and their associations. They also provide an API explorer which is a blessing when you are working around a lot of APIs.
Loopback also has Android and iOS SDKs which make the implementations of your server models in your app a breeze. This removes the burden of having to write your custom implementation of syncing data between your client (mobile apps etc) and server. Something akin to Parse.
Express is a very minimalistic framework which means you have to spend a lot of time in tweaking it for your use. Loopback comes bundled with most of the frequently implemented features like Authentication, User management, and Push Notifications out of the box.