Yea it's whatever you prefer and find easier. I have 3 trip meters on mine, one just shows mileage on the dash, the other two show mileage and average MPG over that distance, so I use one per tank (that way I can see how accurate the trip computer is) and the other I reset every long trip just to see what MPG'S I get per trip, and calculate the cost of that trip.
As Draigflag say's whatever you find best is the best for you.
I personally use the Odometer reading, I just write it down on the fuel receipt ready for input later, which may be days or weeks, but as long as I have the receipt with the Odometer reading on it, i'm fine.
I do reset the trip meter on each fuel up as well, as I like to keep an eye on both the trip figure and the miles to empty figure, this gives me a good idea of how i'm doing during the current tank.
I've done both. I settled on trip mileage for laziness and less digits to enter. I'm trading cars today and debating how to go with the new one. I'm thinking rather than reset both A and B each time I may reset A each time but let B run for several fills. Not sure why that's a good idea but maybe something will come to me.
2019 Hyundai Sonata SEL white/champagne