What are the best headless browsers?

I'd recommend chrome(ium) headless https://developer.chrome.com/docs/chromium/headless . It works with various drivers like puppeteer, selenium and playwright for some added convenience.

At https://checklyhq.com we and our customers use it heavily and reliably through playwright for various monitoring, testing and automation use cases.

As you want to use it from an Agent you also should take a look at https://developer.chrome.com/blog/chrome-devtools-mcp and https://github.com/microsoft/playwright-mcp

I’d separate “best engine” from “best developer experience”. If you want something that mostly just works, Playwright is still the easiest default.

The one in gstack is pretty nice, built off playwright.