I really doubt either is tubular, but the Addco might be. The ST is not tubular unless they changed their design. I know of no aftermarket company that makes a tubular sway bar. I've installed the ST, old school Neuspeed (28mm), and the Progress bar. All were solid.
Out of all of them, I'd recommend the Progress bar. We're going to post a buy on my custom sway bars pretty soon, though. However, I doubt many of you will be able to stomach the price.
http://www.preludeonline.com/showthread.php?t=208228