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
If you're writing lots of custom controls I would choose WPF. Part of WPF's design is to be extendable, composable and the result is that it's dirt simple to write custom controls.
I've done a bit of custom control writing in WinForms and it can be very challanging at time. Layout will really take some time away from you. Several weekends of my life were paid to WinForm Control Layout. Writing the equivalent controls in WPF was a cinch.