This is, in my opinion a matter of how much you use midi. Cubase is vastly superior when midi is concerned, and the difference in audio quality is nominal from what I can hear.
I have to admit I don't have much experience with pro tools, and my preferred daw is Cubase.
So, if you work with audio mostly, it's a matter of how the different daws handle workflow. If you're working with midi, Cubase would be my choice.