CO does not operate the BF service to UIO. The IAH-UIO flight is operated on a 752, so you get the BF seat, but it is regular service (similar to transcon). And the 752 is only some of the time. Other times the flight is a 73G. And since it is not marketed as BF you have no recourse if you get the substitution. It looks like the DL flight is on a 757 from ATL. I don't know that DL has any of their 757s configured for the long-haul international runs, so I don't know what the seats are like, but SeatGuru seems to indicate only domestic-style seats on the DL 757s, so I'd check the schedule for the day you're planning and if CO has the 752 on the route go that way; definitely a more comfortable seat.

S.