If there are good UA options to get you either a) to your destination or b) close enough to your destination that you'll have multiple options to get you there, it makes the most sense to book the cheapest option in the class you want almost hoping for a schedule change, which is almost inevitable if you book far enough out. The challenge comes when you're going somewhere where UA doesn't have great coverage where a schedule change can leave you without any options. Trying to visit Central Asia, the Middle East, most of Africa, etc., becomes far more difficult, so I tend to book those types of flights with long layovers so that an hour or two schedule adjustment will not throw everything off.