My general advice, which is applicable here, is that being in the best cabin onboard a plane is preferable when possible. On Rouge, you're flying in the front of the plane, on AC you're flying in the middle. Rouge will tend to focus service on PE, AC will focus service on J.

It's not just an AC thing. BA J is better on planes without F, so is EK J, UA J, etc... Just seems that crew mentality is to spend the most time on the highest level of service, so I'd book based on that when it's applicable.

Edit: Having flown both, I'd chose Rouge service over AC in PE. The only thing that comes to mind favouring AC would be seatback IFE.