David (the OP) asked about the difference between the Sweet 16 and the 3520B - for the most part, we've been discussing the merits of the AB - not a fair comparison lathe to lathe, but the Sweet 16 has it's own feature set in addition to the intangibles that Robust offers. Stainless ways, the ability to remove the bed section for greater swing (32" total over the ways) and easy extension of the ways for longer spindles. On the other hand, you're giving up a sliding headstock and the ability to fit a tilt-away for the tailstock.
I'd have to ask myself if American made, better build quality and the best customer service on the planet is enough...with that said, the difference in price between the Sweet 16 and the AB25 is only $700. I'd go for the American Beauty...again.