Either way you slice it, a Punk return adds a ton of intrigue wherever he sets up camp.
If he goes to Raw, I'd argue that Punk-Rollins doesn't need the belt to amplify the feud. You can do much more with a Priest cash in/championship run or a Balor/McDonagh briefcase bait and switch in which you have Balor holding the belt to amplify the JD story. I still think it would be really cool to see a "Judgment Day Black" and "Judgement Day Purple" splinter of the stable like they did with nWo with Priest, Ripley, and Dom on one side with Balor, JD, and TBD on the other (Liv Morgan maybe?) with Priest's side the faces in the story. Or you just have Priest lonely wolf it and go in to Mania as the face against Balor.
If they go that route, I'd just have Gunther dominate the midcard a few more weeks. Have him cut a promo a couple weeks before the Rumble to the degree of "I've beaten everyone and everybody at this level, and to prove I'm the best, I'm entering myself #1 in the Rumble and finish what I started last year", but have him be eliminated due to Gable hijinks to kick off that story again. Gable goes over at Mania and Gunther comes back around Summerslam and wrecks shit and becomes champion then beating Balor/Priest.