Preferred Vector Image format for use in WPF?
The preferred vector image format is XAML. There are a lot of ways for a designer to generate those graphics. Adoble Illustrator for example can use the XAML exporter. The open source tool Inkscape can export to XAML directly, a designer can also draw XAML using Microsoft Expression Design and Microsoft Expression Blend. Literally all vector graphics tool support SVG and there are a lot of ways to convert SVG to XAML.
Don't bother with WMF/EMF it will just look ugly since windows can not render them antialiased.