Bun is miles better in this regard.
Deno initially did not even want to focus on Node/NPM compatibility, and then backtracked once they understood the importance of it.
Bun OTOH runs the entire Node.js test suite on every commit, and the mentality of breaking less existing node/npm code is clear. e.g, just in this release, `bun publish` has the exact same CLI as `npm publish`, and bun also works out of the box with .npmrc.
About the Node.js test suite.. many modules are at 100% compatibility, and many are at 90%. You can track it here: https://bun.sh/docs/runtime/nodejs-apis
Also, they reimplement the V8 public C++ API in JavaScriptCore (!) so that packages like npmjs.com/cpu-features work [1]
Every new feature has this aspect to it, e.g the postgres client inbuilt is a drop-in replacement for the `postgres` package.
As far as Node/NPM compatibility, and thought given to compatibility in general, is concerned, there is absolutely no contest.
And if I'm allowed a little snarky slight... Deno couldn't even maintain compatibility with their own API for reading and writing files during the Deno 1->2 update.
[1]: https://bun.sh/blog/how-bun-supports-v8-apis-without-using-v...