I assume smaller because you can see the entire board a bit easier and it takes less time to scan.
Which gives you a better perspective?
And then how big is too big and how small is too small?
Make the board as big as you can fit on the screen for slower games (>7min.) Smaller for fast games.
That's why playing hyper on a phone is insane fun
I have to switch sizes depending on if I'm wearing my glasses or not.
I remember a quote from a movie once that was something along the lines of chess is a game you play in your head not on a board.
What that means is the size of the board or what the pieces look like shouldn't matter. The board is just the physical representation of the calculations and ideas in your head. In fact, it would probably make you a stronger player in the long run to pick the most difficult board settings. Learn to calculate without looking at the board and you'll be better off for it.