Feather mining (the style that uses the 1x1 branches) is more efficient per block mined, but it requires a lot more attention compared to a straight 2x1 hole because of all the turning you need to do. So 2x1 is what most people do. People who have enough resources to make beacons usually speed-mine instead, though. That's because with a beacon giving you Haste II and an Efficiency V pickaxe, you can mine stone blocks instantly, allowing you to clear out 2-tall spaces rapidly. This destroys more blocks per ore but is much faster than anything else in terms of time. That said, in the 1.18 update, diamond ore can only be found at levels where deepslate generates instead of stone. Deepslate cannot be instant-mined, so caving is once again the most efficient way to find ores. I consider this more fun than the old style of mining, so I'm glad they made this change.