For training, I put everything I can onto each of the pages available on my Garmin 510.
I like to be able to scroll through the pages and see various metrics during training, etc.
For racing, I have a dedicated page that shows 1s Power, Speed, Cadence, Time.
Four fields makes the text big enough to see at a glance.
I've found that having my HR on my 'race' screen is counterproductive. Looking down and seeing 194bpm for 45 minutes is scary.
I also have a specific interval page that shows 10s Power, Cadence, Lap Time, Power Zone.
When doing intervals or a specific workout, I do better with 10s power and lack of speed.