If you're storing the car, then it's best to maximize the range by (a) keeping the batteries at a mid-range charge level where deterioration is minimized, and (b) minimizing charge cycles. Storage mode allows the batteries to slowly discharge to a low-ish level - but not too low because that also degrades the batteries faster - and then tops them up as needed to maintain the batteries in that sweet spot.
If you're driving the car, then it is best to use Standard mode. You don't want the batteries sitting at 100% because that degrades them faster over time, so Standard mode charges them to 90%. It's also less stressful on the batteries to discharge them at a higher SOC, because at low charge levels the output voltage is lower and you have to draw more current to achieve the same power level. So keeping them at 30% is not a good idea - better to recharge them to 90%.