I would suggest central mine to rule them all - a public cobweb mine.
Entrance can be as fancy as you want, but I suggest simple 1x1 watervator starting at y = 17, as there would be mine lower.
On beginning lets have floor at y = 11 (a lot of lava is at y = 11 and below) and ceiling at y = 17 (17th layer and higher doesn't contain diamonds).
Later we could lower floor to y = 5 - at this layer and lower bedrock is spawning.
Main corridors would be 4x4 squares with overlapping corners going like "X".
Helper tunnels would go like "+" from central watervator. It would be 2 block high, as they would be well just helpers.
Here are various
plans of it, and
there is ore analyzes, so we know where to dig.
This mine is best mine, if you want it to stay in relatively one place, and if you want to mine all ores in hat area.