I used to have a Dash (briefly) before returning back to the BB family (Curve). In my opinion, the Dash has clearer pictures, but that's all that it has over the Curve. I HATE Windows based phones. Everytime you are running multiple applications, you have to stop, go to Task Manager and stop other apps.
Additionally, the buttons are too small in my opinion once again to type normally. Most of my emails or text messages came out like this:
heyt whatsa upp, sorryu forr thee typpinge errore butt mye buttonas are toop smalla.
You get my point --small buttons.