I Personally feel that a 13 X 4 is very unappealing, and considering that the Brawl Roster tended to shift around after Characters started to be unlocked, here is my 10 X 5 Roster:
1st Row:
Mario, Luigi, Peach, Rosalina, Bowser, Yoshi, Wario Donkey Kong, Diddy Kong, King K.Rool
2nd Row:
Link, Zelda, Shiek, Ganondorf, Toon Link, Impa, Ice Climbers, Samus, Zero Suit Samus, Ridley
3rd Row:
Kirby, Meta Knight, King Dedede, Olimar, Villager, Ness, Captain Falcon, Fox, Falco, Wolf
4th Row:
Pikachu, Jigglypuff, Mewtwo, Charizard, Lucario, Greninja, Shulk, Marth, Ike, Chrom
5th Row:
Pit, Palutena, Little Mac, Wii Fit Trainer, Marshal, Mr. Game & Watch, Snake, Sonic, Mega Man, Pac-Man
in the 6th row of the 1st column, Mii Fighters,
in the 6th row of the 10th column, Random
DLC fills in columns 2-9 of the 6th Row