For a brand new application, is it better to use WPF over Windows Forms? I used Windows Forms before but not much WPF. As far as I know, WPF is the successor to Windows Form
In this case, I'd say follow the lead of your Vendor (i.e. Microsoft). Their own internal production increasingly features WPF; and it's scope (think Silverlight) and depth are clearly greater than WinForms. They also use it increasingly with reference to Best Practices. From all the evidence (here and elsewhere), it appears to be ready for Prime Time developement.
You have epressed no particular affinity for WinForms (I would guess what there is is based on familiarity). You'll need to switch eventually. A new project would be a great place to start the process, everything else being equal.