When comparing CanJS vs Preact, the Slant community recommends Preact for most people. In the question“What are the best lightweight JavaScript frontend MV* frameworks?” Preact is ranked 3rd while CanJS is ranked 7th. The most important reason people chose Preact is:
The size when gzipped is only 3kb, and performance is as good as (or even faster than) React itself.
Specs
Ranked in these QuestionsQuestion Ranking
Pros
Pro Fast rendering
Update of single element, no diff like react.
Pro Compact and easy syntax
CanJS has an easy to learn syntax.
Pro Lightweight
The size when gzipped is only 3kb, and performance is as good as (or even faster than) React itself.
Pro Same API as react
Avoids having to learn an entire new paradigm, and makes it easy to switch between the two libraries later on.
Pro Lots of examples and libraries
They have a bunch of examples and addon libraries.
Pro Awesome CLI
Preact CLI gives you a perfect scoring PWA out-of-the-box with no configuration.
Cons
Con Hard to find resources outside of the official ones
Since CanJS is not very popular, it can be hard to find learning resources, tutorials, guides or any other resource that may help development.
Con Difficult to learn
You need to be good in React JS first to learn Preact. Documentation is not rich. And some of the examples given on site are not working. Developers are not much active on Stack Overflow as well.