Conversely, if you fly mostly full fare economy, DL may be the way to go. They give out more free upgrades than AA but they place more restrictions on using them. The biggest restriction is that you can't use them with most discount fares. If you pay full fare (or near-full fare), you're only competing with other people who have paid the same, so you'll have less competition for the upgrade seats. On AA, since any fare can be upgraded, you'll have higher-level elites on cheap fares in front of you.