I have Boost, AFR, Oil Temp, Charge Air Temp, Ign. Correction 1, Ign. Correction 4.
Ran OAR for a couple weeks until I was confident that Shell 93 (only gas I use) was running well with my tune. After that, I don't think it's useful to keep on your screen unless you regularly fill up at different stations.
I only run Ign. Correction for 1 & 4 because the firing order is 1-3-4-2, so I'm seeing every other cycle. You can run all 4 if you want but I don't really think it's needed, and it frees up two more spaces to monitor other things.
I like having Oil Temp for the same reason I run Boost, I like to see an exact number instead of a vague approximation. In any case, you can use it for a while to figure out what temps correspond to the needle positions on the factory gauge (150* is about 1/4, 200* is about 1/2) and then just use the factory gauge for an at-a-glance reference.
Charge Air Temp is good especially if you're still on the stock intercooler, because it heats up very quickly.