This isn't so much a "trip report" as it is a complaint. I flew CO 1993 CLE-IAH on 7/14/01. It was on a 737-300. Now, I have been on United and US Airways 733's before and CO's 733 was the most uncomfortable. I thought it was an isolated incident, as I have been hearing good things about CO. However, I learn I was wrong on the return trip. On 7/22/01 I flew IAH-CLE on 1535, a 757. I thought this would have to be a more comfortable aircraft. I was wrong again. CO has the most uncomfortable seat of any airline I have been on. I am disappointed with that. However, to there credit, we were on-time and the ground staff and flight attendants were friendly.