PHPSpec is a SpecBDD tool more dedicated to guide you in code design rather than a testing framework. It depends what you expect from tool and if you want to make a proper TDD/SpecBDD it's easier to use PHPSpec because it was created to help developers write readable and well designed code.
Remember that TDD/SpecBDD is not about testing all edge cases or doing whole-application-integration testing. It's about writing specifications for small units of code.
Few days ago I gave a talk on it, here you can find slides: http://www.slideshare.net/cakper/2013-0613-spug-spec-bdd-in-php I hope it will be useful to make a decision.