We bought Conn sousaphones recently. They've been trouble.

Our Yamaha sousaphones are still going strong and are at least 12 years old. There's a design flaw/weak point where the valve stem screws into the piston, I have to deal with that breaking a few times each year, but otherwise they've been solid workhorses. If I was buying again I would buy Yamaha.

A few friends have Jupiter sousaphones and hate them.