which wrist would give the most accurate reading with Apple Watch?

The Apple Watch does not know if you are standing walking back and forth in a short hallway where GPS will not kick in. It just sees the accelerator activity from your moving arm. You are Right handed, so you most likely move that arm more than your Left arm.

I once got standing credit laying in bed, by actively waving my arm. I was just tricking the accelerator into thinking I was up and moving, so it gave me credit for standing. I also often juggle 3 bean bags to get standing credit in about 30 seconds, instead of actually walking around for 2 minutes. Again just accelerator tricking (I do enjoy the juggling though 🤹‍♂️)

Either could be correct, depending on your activity and how you are moving your arms. The watch uses (amongst others things) the accelerometer to detect activity so it is looking for the natural arm swing from walking. This means if the watch is on an arm which is moving a lot but you are not walking (maybe operating something like a hand pump) you will get a false high value. If you are walking but not moving the arm (pushing a bicycle or stroller) you will get a false low value. If you are driving and conducting the music from the car radio you may get some mileage from that too!

When it comes to counting steps and calories, you'll most likely get the most accurate reading on your left (non dominant) wrist. Since the watch senses movement, and you're more likely to perform small tasks with your dominant arm, there is a higher probability that it will count things as activity that shouldn't be counted.

It may read a little lower than actual (no fitness tracker is perfect), but if you're shooting for a goal, better underestimate your activity than overestimate it.

I wear mine on my right wrist. And have no issues.