personally for me, temp, just because my oil temp gets dangerously high.
also it tells you when its safe to rag it, and its a LOT later than when your water temp is up to normal temp, thats for sure.

if oil pressure drops much the engines dead anyhow, so i just ignore that, its paranoia, and not loads better than the red light on your dash imho.

gauges to view while driving hard are utterly pointless in a fast car or a car you using on track, as you have no time to look at them.
even checking what boost your cars holding on a car with mega power is next to impossible in a straight line.
hard use on track or drifting even a rev counter is barely of use as you got better things to concentrate on.

something with a peak recall facility would be your most useful thing unless you just want it for looks and to show off on passionford.