I have a Husqvarna/Viking Designer Topaz 20 - it sews thru so many layers of denim I couldn't believe it. When I was visiting my friend in AZ she was sewing thru various fabrics making a pool/awning thing and her Bernina wasn't going thru it and so I said to try my Designer. It sent thru with no hesitation. I don't sew much using denim or any heavy fabrics - I have the Designer for it's embroidery ability. But a few times it came in handy.
Good luck with your choice.