Polymer Starter Kit vs Polymer App Toolbox

What's the difference between Polymer Starter Kit and Polymer App Toolbox?

Both are collections of web components, build & testing tools, and Material Design templates for building Progressive Web Apps with Polymer.

Which one should I base my new project on?

Here are some details regarding both of them:

Toolbox

Pros:

• Was built after Polymer team started focusing on app side of Polymer rather than elements
• Gets more updates than PSK
• Has all the other required tools (server, linter, bower, tester) built-in
• In case of building an element (like to publish) it uses flat import structure, where even though bower downloads are kept in bower_components folder and element to be made is kept outside the bower_components folder imports are still made as though both are present in bower_components
• Is made specifically to help developers in building their application/element
• Is more in line with Progressive Web app vision of the team.

Cons:

Still in beta phase just like all the app-elements it uses internally

PSK

PSK was built with the purpose of providing a starting point for the developers who are new to Polymer and are more in learning phase. It has some pre-built elements with hard-coded data. If you look inside index.html you will find <template is="dom-bind"> being used which Polymer team recommends not to use in production environment. It was built when Polymer team was still focusing more on the elements side of Polymer as a result it does not use any of the Polymer's app-elements using which Polymer team has built the shop demo. A newer version has not been released since March as team is currently working on version 2 of PSK.