If money and resources are no object then (IMHO) the client is almost certainly one who will feel most comfortable with Oracle. So if it's a sales pitch you're after, it's a no brainer. They may not *need* Oracle, but they'll feel better about that choice.
The only exception is if it happens to be a company that values OpenSource-ness; then the technical questions of which is actually more appropriate come into play. I think others have covered this well enough; the only thing I would add is that AFAIK there are more and better add-on tools for Oracle to make programmer's lives easier, which in the long run is better for the client too.
