This might be a silly question, but do most of you try to trigger from a certain channel each time you use a trigger?  I suppose it doesn't make much difference, except to keep things simple in your own screen saves.  Any thoughts?

I trigger based on what I need.  By signal rather than channel.  The effective use of trigger can really help you get the capture you are after.  

If I want to trigger off of a snap accel, for example, I would use the channel that has secondary and adjust the level to a higher KV so it triggers on the KV spike you get on a snap throttle.  

Also, if you think you know what is failing, you can trigger on that signal with the relevant inputs that are needed for that signal on the other channels.  Then when that signal fails, the scope will stop and you can see if the other signals went down also.

Don't limit your use of trigger but allow yourself to use it creatively to make the scope do what you want for a given situation.  Maybe you want single trigger to catch one event, maybe you want a delay to position the waveform on the screen, or a positive slope at a certain voltage.  Maybe the capture is more stable triggering off a signal on channel B.  There are a lot of ways to use trigger to get desired results.  Let yourself go  ;)