Really been wondering this myself.. Very hard to say honestly and I'm not completely sure.
Some people say War Ichigo because he beat Yhwach who beat Aizen, but those people seem to forget, Aizen is back in base during the Blood War arc.. The Hogyoku took his powers back.. So there's no confirmation that Prime Yhwach > Prime Aizen
And note that Dangai Ichigo was straight up toying with Aizen while War Ichigo was struggling the whole fight with Yhwach.. Like the actual storyline leads me to believe War Ichigo would be stronger since he has his "true" zanpakuto(s)... But Dangai Ichigo was just so damn monstrous that he stood in a higher dimension than God Level Aizen...
As far as I remember, War Ichigo's Gran Ray Tensho didn't seem nearly as powerful as Mugetsu, but he's got a bigger variety of powers in War form.
OT: I dunno but I hope this comment makes people think!