Stegosaurus vs Baryonyx

Baryonyx walkeri is pretty problematic, we can't speculate its size too much, but it for sure wasn't the same size as the immature specimen. I'll say it's close.

Well-armoured herbivores tend to have the upper hand over theropods of a comparable size, so I would probably say Stegosaurus. But since the adult size of Baeyonyx can't be estimated with our current findings its hard to say who would win officially.

I'll not say anything on size.

But make no mistake, in a completely hypothetical scenario where a spinosaurid that naturally grew to the same weight as a particular stegosaurid were to find itself in a fight to the death against one, the former better have butterflies in its stomach.