What are you trying to do with the engine and the RIP... if you do or plan to do variable data, the Creo is much better.
Built in Impo on the Creo is better, Fiery hardware is older and expensive to upgrade. Color seems more stable on the Creo over long runs and is easily matched on a rerun. Both will do simple RIP and imposition but overall the Creo is faster and more dependable. BUt usually has a longer learning curve to master. I spec Creo if both are available.