My list of CO peeves:

1. Domestic upgrades are haphazard. Supposedly they are electronic. In reality CO revenue management holds all upgrade seats open until the last minute, even for elites and releases them at the airport. A scrappy silver or Gold can trump a platinum by timing checkin at the airport properly. This sux.

2. Most of the routes that CO used to fly with big aircraft with First class seats are now being replaced with smaller regional jets with no first class cabin (Embraer RJ jets). This is especially horrendous in CLE. See posts by duxfan in the CO forum for details. What is the use of being elite in CO if you have a good chance of flying on a regional jet for 3 hours with no FC cabin?

3. International upgrades are impossible. Elites often get trumped by CO employee non-revs at the gate because of a stupid 72 hour rule initiated by CO. This means that upgrades within 3 days of departure are forbidden with miles. Basically this 72 hr rule is just a way for Co employees to easily get biz seats for themselves. Even harder still is to get reward seats internationally using full miles (no upgrades). Also if you want to use miles to upgrade you have to either pay one of the more expensive fares (HOKEY) or pay what is known as BendForward fares (an extra $400 or so for each segment) and then hope and pray that your upgrade clears before the 72 hour mark. If not then you're out of luck -- you don't get a refund of the $400 extra you fork over either.

4. CO doesn't release many reward seats for domestic or international travel. You will find that you have to travel to other low-traffic airports or be flexible on choice of days. Furthermore there is no way to check availability of reward seats online.

Many many more: for a good laugh, go to the CO forum and search on "HOKEY, BendForward, 72 hour, 30 day rule, international upgrade and EUA".

Go for a winner -- go for AA.