Have flown Continental to Guatemala via Houston (3 years ago) without any problems - certainly none in transit at Houston - and have used both airlines on east coast transatlantic flights over past few years. I think both airlines charge for drinks now and poor in flight service seems to be prevalent on US based airlines (probably as most have been in bankruptcy in recent years, there is not a lot of staff morale). If there is little to decide in price, I would opt for the airline that can offer the most convenient timings/shortest overall travel time.