You are specifically interested in the seat. Depending on the Italy route, both BA and IB are heavy users of the Airbus A320 series of aircraft for shorthaul. There are some variations but most seats on most aircraft are the same, and were ordered centrally by IAG with some intention of interchanging aircraft between the OpCos at some point. I suspect that is wishful thinking, but it does explain why the aircraft equipment signage on BA has Spanish as a second language, when I suspect there are more Welsh speaking customers on BA. By definition it sounds like the hop to Italy will be fairly short, so personally I would go for the usual combination of fare versus timetable, rather than trying to rank BA over or below IB.