As a 2P or 1P you're going to have the most challenges with upgrades on hub to hub routes (domestic or international), and hub to spoke international routes over hub to spoke domestic routes.

If most of your flying is hub to spoke domestic routes, then your luck upgrading even as a 2P should be quite good.

Of course, using miles to upgrades, CR1's or SWU's is always your best bet since you can confirm them at the time of booking. If you're a 2P and want to upgrade using miles and there's upgrade inventory available - it's yours, no matter what.

- T