In city driving, I tend to watch current average, or today average, since that's the goal I'm focused on. Cruising, I watch Instant because it helps most for driving with load (DWL).
My biggest improvement to the SG would be to have the ability to show Instant and Current AVG on the same screens. That would save me having to flip back and forth.
On the 4 gauges screen, I switch that one around a fair bit: I keep an eye on FWT and VLT (on the occasions I'm driving without the alternator). Also RPM, since the car has no tach. I'll probably start watching intake air temp again, as it'll soon be time to hook up the HAI again.
I leave the screen in instantaneous 'gauge' mode while driving (checking my tank avg after each leg of my commute). I've experimented over the last year with what four things to watch, currently set to: