I mine top to bottom unless there is another person in the mine and I don't have trench yet. Then I would go to a level below them, but not bottom, and mine. I mine in the same manner with and without trench, which is 4 blocks deep, walking side to side.
Although trench is a blessing and is satisfying, I hate it. I prefer to mine in the default way, 1 block at a time. But the competitive nature of mining top forces me to use it >;{
2 > 3, like actually, it is
When you mine 2 tall, the mine doesn't get emptied as quickly meaning you can get more exp, mining exp, and mana per mine reset. The money will be about the same, only about 10% different, which is about 2.5m every 15-20 minutes in titan. Very minimal loss when you're at titan/god mines.
It's also more considerate for other miners. If all of the mines are full of people, you will be more fairly sharing the blocks. If it's not busy but you leave 1/2 way through, there is more of the mine for the other miners.