Compare two (or more) tools that are trying to solve a similar set of problems, without discussing any of the following:
- Programming Language
- Stars/Forks/Downloads/Issues/PRs/Stack Overflow Answers/etc
- Age/Maturity of tool
- Users of tool/Who the tool is made by
- Existing comparisons
- Your or someone else's personal experiences
And do it without trashing either tool. Try to say things that the maintainers of both tools would agree with.
Focus on things that distinguish the tools from one another rather than rehashing everything there is to know about the tools.
In short, make your own abstract technical/architectural comparison.
React & Preact are both tools for building user interfaces using trees of components.
React focuses on creating a programming model which enables developers to build better user experiences. It tends to be focused on the performance of larger, long-runing apps. The core library of React is abstracted away from the Web so you can build React "Native" apps on iOS & Android and share code between them all.
Preact is designed to be mostly API compatible with React with a much smaller bundle size, focusing on startup time performance, partially by cutting out some features of React. Many of the features of React are available in other libraries so you can "pay as you go" with bundle size. Preact tends to be a better choice for mobile web apps in where startup performance is paramount.