I don't think any airline is going to guarantee you upgrades from cheap fares, particularly at peak times, if that's what you're looking for. I have four Europe trips in Jan/Feb that have all been upgraded with AA systemwides, but this is off season and there's plenty of upgrade inventory if you can pick and choose among dates and flights. I've cleared every upgrade request since I started flying them in 2002 and I'm happy there, including SFO-FRA this week on a $321 base fare.