The best PS2 emulator for Chromebook is PCSX2, if your Chromebook supports Linux apps and has strong enough hardware. PCSX2 is open source, works on Linux, and gives better compatibility, settings, save states, widescreen patches, and performance control than most other options.
AetherSX2 and NetherSX2 can be mentioned as Android based options for some Chromebooks, but they should not be the main recommendation. They may work on certain models with Android app support, but results depend on the Chromebook chip, Android support, and emulator version. For most Intel or AMD Chromebooks, PCSX2 through Linux is the better route.