When comparing Koa vs Rocket, the Slant community recommends Rocket for most people. In the question“What are the best backend web frameworks?” Rocket is ranked 14th while Koa is ranked 33rd. The most important reason people chose Rocket is:
Rocket makes extensive use of Rust's code generation tools to provide a clean API.
Specs
Ranked in these QuestionsQuestion Ranking
Pros
Pro Generator support from ground up
Using generators (a bleeding edge feature, even for Node.js) would clean up your code from the mess caused by all those callbacks; making your code more manageable.
Pro Extremely lightweight
Koa is very lightweight with just 550 lines of code.
Pro async/await keywords are supported and has transcended beyond generator functions
Generators functions are of course a huge plus, but at the time Koa team has transcended generations functions and shifted towards async/await style programming. It has made the Koa best framework available in the market.
Pro Development team has a proven track record
Koa is developed by the team behind a widely used node.js framework (express.js).

Pro Built for ES6
Pro Easy To Use
Rocket makes extensive use of Rust's code generation tools to provide a clean API.
Pro Streams
Rocket streams all incoming and outgoing data, so size isn't a concern.
Pro Cookies
View, add, or remove cookies, with or without encryption, without hassle.
Pro Testing Library
Unit test your applications with ease using the built-in testing library.
Pro Extensible
Easily create your own primitives that any Rocket application can use.
Pro Templating
Rocket makes rendering templates a breeze with built-in templating support.
Pro Query Strings
Handling query strings and parameters is type-safe and easy in Rocket.
Pro Type Safe
From request to response Rocket ensures that your types mean something.
Pro Boilerplate Free
Spend your time writing code that really matters, and let Rocket generate the rest.
Pro Config Environments
Configure your application your way for development, staging, and production.
Cons
Con Community is relatively small
Con Not compatible with express style middleware
Koa uses generators which are not compatible with any other type of Node.js framework middleware.
Con Has no routes separated by HTTP method or URL pattern
Con Wrong Middle ware, security issue
Con Abandoned
Con Nightly
Uses only nightly versions of Rust.
