WPF is much better if you're targeting screens with high or variable DPI. It's also (when you've built up the experience) a better way of implementing complex forms. WPF stylability it also very nice making it easier to customise controls if your bosses give the marketing department too much creative flexibility. However WPF is not a panacea and comes with a steep learning curve. As the saying goes 'WPF makes easy things hard and hard things easy'.
If you're just knocking out simple forms for simple applications the overhead of WPF is a disadvantage and will slow development. However for larger projects with complex forms the power of WPF will probably allow an experienced WPF developer to complete the project faster.
Some more thoughts here.
NB: I'm not an advocate of either particularly. I've used both and will continue using Winforms for our legacy projects. But as/when new projects are started we go with WPF now. We have the experience and toolbox of useful classes and WPF seems to offer a more powerful experience. We supplement both with DevExpress controls.
Biting the hand that feeds IT
