I disagree with AdamFrisch. The only rule is that there are no hard and fast rules. Some planes within a fleet are new, others are old. Some have new IFE, some have old, and some with new IFE may have a glitch that prevents it from working on your particular flight. Sometimes the wait at Immigration is short, sometimes long. Sometimes the plane will clean, other times there will be crumbs left in the seat pocket. Sometimes the food is good, other times it is excerable. Sometimes the flight attendants are accommodating and competent, other times they may be less so.
The only things that are constant are:
1. A connecting flight will likely take longer than a non-stop, and there may always be something that happens with the connection.
2. A flight that costs less leaves you with more money in your pocket.
It is up to you to decide whether the possibility of any any feature mentioned in the first paragaph of this post trumps the certainty of the last two features.