I'm planning to travel to Japan later this year, and can choose either United or ANA. For my possible travel dates, the airfares are comparable. I'd like to use some of my MANY plus points for this trip. Since ANA is one of the few partner airlines where I can do so, I'm wondering whether my chances of eventually getting an upgrade confirmed would be better if I buy the ticket from UA as a codeshare rather than buying the ticket from ANA. Or are the chances exactly the same?