I fly with AA and have had really good luck using mileage upgrades internationally. As stated above, they allow upgrades on any fare, and that is a big plus for me. I wouldn't fly an airline that tried to upsell people into higher fare classes to use upgrades.

Of course you're not going to get free upgrades domestically. Personally, I think it's a good tradeoff. Domestic first class isn't nearly as good as international business, and it isn't as important either because the flights are usually shorter. On longer flights I'll upgrade with my stickers, on shorter flights I'm fine with AA's MRTC.

But I'd rather sit in coach on a 3 hour domestic flight and be able to upgrade on a 10 hour international flight, versus sit in FC domestically but coach internationally. Furthermore, at least with AA, upgrades to business can use international arrivals lounges, which worked out really well for me 2 weeks ago at CDG.

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