I like that angular look to the Bryce rendered version. Maybe a low angle smooth to round out the round parts but leave the edges intact.

Carrara's looks to have better lighting, Bryce's looks to be more accurate. Abiout what I'd expect from a side by side.

What quality level did you use for the Bryce HDRI?

EDIT - were the windows on the Bryce render left opaque on purpose?

Friends don't let friends use booleans.