At my house we had some very heavy gates made up by a professional builder and we didn't want it to move. The frame was made of galvanised steel and it was covered with heavy kwila riveted to the the steel frame. So far so good.
However another gate made of pine for the back of the house by the same builder started off perfect, but winter weather has caused it to sag slightly despite the diagonal brace. I can tell you with all certainty that the way you place the brace will make no difference.
You're splitting hairs. What you'll find is your gate will move even though you've braced it. We were told this by our builder and I know it to be true of all wood as I've done a fair amount of wood working.
The reason is, it's because it's made of wood. Wood expands and contracts with the weather and the seasons. So if you don't want it to move, make it out of metal.
If you want it to move less, make it out of a something like cedar. Down here in NZ we make a lot of gates and fencing out of treated pine. It moves and twists all over the place.
I'd start by making sure your wood is dry. A lot of the timber you get from the merchant is often stored outside and isn't nice and dry. You may need to dry your timber out for a month by stacking it nice and flat off the ground and out of the rain. Turn it, allow airflow through it. Then when it's dry you can start making your gate.
You've got a couple of options. Do any of the diagonal brace options you've already asked about. Or, us Ecnerwal's suggestion with a turn buckle. It's a sensible idea. The reason is you can adjust the tension to move the gate up or down as it moves... and it will move.
Also, to help slow down the uptake of moisture into and out of the wood causing it to move you can paint it or oil it.