I recommend the HO Formula 2 tube. It is being sold for $199 by
several sources. We've had one for 4 seasons and have never had a problem with it. As you can see from the video below (that's not us!) it is very hard to flip, even with extreme bouncing.
The seating cutouts are long and let you sit completely inside and hold the handles which makes it a very comfortable ride compared to other tubes.
Here is ours off of Bear Island: