If we're talking about the Predator from the original film, then definitely the Predator, even against Ripley at her best.
But as that franchise wears on, the Predator gets watered down more and more. It took The Terminator, Apollo Creed, and Jesse the Body (not really, but you get the hyperbole) to stop the Predator in the first film. By the second film, we had fallen to Danny Glover, Gary Busey, and Bill Paxon stopping a Predator. The Predator, released last year, was essentially an action comedy driven by garbage CGI.