Bernese Oberland
In the past, I lived in Lauterbrunnen for around 18 months. I found the area to be varied and rewarding for speedflying, especially for hike-and-fly.
With many valleys, there is a great range of slope aspects for reliable flying.
The biggest hike-and-flys such as Ostegghütte, Silberhorn and Rottalhütte have quite demanding launches. Keep this in mind if you are a group with less-experienced pilots. Despite this, there are also many areas that are some of the most beginner-friendly, such as Grimmialp.
See the Google Earth project for information about all of the areas that I like to fly speedwings.