I almost always share with the person if needed. I have a smaller bag that holds my ipad, headphones, etc, that slips into my backpack that I use for at the seat. I then usually place both my back pack and roller bag in the overhead. I follow you though. If you are polite, you'll receive the same in kind. If I had to chose I'd say window though so that person doesn't have to keep interrupting the aisle seat.