It all depends on what you do with the vehicle. If you tow then a trans temp gauge is handy, performance beyond basic bolt ons can benefit from an AFR gauge for better tuning capabilities. If you're stock then save your money unless you just really want to know, then get a trinity and enjoy both performance gains and an instant readout for the same price as an intune and gauge.
My old truck ran an AFR gauge, fuel pressure, voltage, nitrous pressure, and a trans temp gauge. My new truck runs/will run a boost, fuel pressure, AFR, nitrous pressure, nitrous management center, and a trans temp.