Here are the number of games played on every different board sizes on DGS (Dragon Go Server):
| Size | CNT | +------+--------+ | 5 | 2464 | | 6 | 466 | | 7 | 11015 | | 8 | 434 | | 9 | 101230 | | 10 | 1256 | | 11 | 3166 | | 12 | 716 | | 13 | 65205 | | 14 | 455 | | 15 | 4656 | | 16 | 315 | | 17 | 1145 | | 18 | 91 | | 19 | 639319 | | 20 | 293 | | 21 | 371 | | 22 | 104 | | 23 | 265 | | 24 | 79 | | 25 | 3657 |
As you can see boards of odd size are much much more popular than boards of even size.
In total: 99.5% of games have been played on boards of odd size, while only 0.5% of games have been played on boards of even size.
There seems to be something severely wrong with boards of even size...
So my first question is: what is the problem with boards of even size?
I also wondered why 19x19 is the number one most popular size for Go boards...
Just like the accepted answer to this question says, the principal reason that the 19x19 board is considered to be the best is that:
it is the largest board size on which there are more points on the sides (under the third line) than in the center (above the fourth line).
But I found that to be inaccurate! The board size with the best balance between territory (on the sides) and influence (in the center) is not 19x19, it's 20x20.
If Black puts all his stones on the third line, and White puts all his stone on the fourth line, then:
On a 19x19 board:
- Under area scoring: Black has 192 points, White has 169 points.
- Under territory scoring: Black has 136 points, White has 121 points.
On a 20x20 board:
- Under area scoring: Black has 204 points, White has 196 points.
- Under territory scoring: Black has 144 points, White has 144 points.
So my second question is: why not a 20x20 board?