Species 8472 vs Data

Fight takes place on the Enterprise.

A Species 8472 tore through the Voyager's hull, iirc and sustained multiple kill-level shots from a Hirogen rifle.

Should be powerful and durable enough to tear Data apart in a H2H match, which I'm assuming since you didn't list weapons.

Well could Data speed be a factor though.

8472 wins. Outside of the godlike beings, easily the most formidable in Star Trek.