Well, your question is really tough as they are very different watches.
The way the chronograph function is displayed, the complications combination, the size, the way the movement is decorated and appears to the wearer...
I guess the live experience is mandatory and you'll just have to ask yourself how does it make you feel.
As Fx said, the Auto versus manual issue is an important one.
I you don't care, the movement of the Datograph is certainly more spectacular and very well finished.
The Patek is more classical in the look (case but also the sunburst dial).
The annual calendar complication on the Patek is an interesting addition to the chronograph function too.
But the Datograph has it very nice oversized date and the Bi-compax layout.
Both are very good choices on an objective basis. Remains the subjective feeling and only you can tell

Keep us informed of your choice!
Cheers, Mark