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
Having just recently done a very similar product (3d viewer for mining data in WPF) I can definitely recommend WPF/SlimDX.
The tools are a bit lax (especially Visual Studio), but WPF makes it much easier to make an app with a bit of Zing, rather than the default control grey that most things have.
Using D3DImage from 3.5SP1 it's very easy to host a SlimDX device inside a control.
Overall I'd say WPF isn't better to use, just different. Some things are better, some are worse. But it's definitely the future.