One thing is that semidwarf trees in my yard all look like standards in other climates. They get big. One consideration is how you will take care of the ground under the trees, if you need room for mowing or whatever. I have ground cover Comfrey, Symphytum ibericum, planted under some fruit trees and it keeps out the weeds and is not too hard to find apples in.

My trees are grouped in rows or in a double row for mowing purposes then I put smaller fruits like currants in between some of the larger trees in a row. Having them grouped makes it easier to put fencing around to keep deer out, too. A circle might make that easier. Another consideration is what other trees are around to cast shade on them or cause root interference. Fig trees in particular need as much full sun as possible.

Rectangular grids can allow the canopies to meet sooner, which means that ladder room is reduced more quickly.

I prefer a triangular spacing or the diamond thing that you mentioned, as long as the diamonds are not rectangles on end.