Never had one but our friend Stacy did at Cheese Cake Factory and said it's the best vegan burger out there and it's not even a contest. She thought they were great. As for me I'll stick with the red meat version.
Haven't had an impossible burger (they are only served in restaurants I think?), but I had a beyond burger a couple months ago. It was good...but I still prefer normal beef. The beyond burger tasted good but it is not quite like beef.