Okay, if we're including levels, I would say:
A Tier:
Mario (2 - 4 levels, moderate chance of a character being added)
Pokemon (1-2 New levels, high chance of 1 - 2 character additions)
Wii Series ( 1 - 3 levels, moderate chance of 1 character addition)
Donkey Kong (1 - 2 levels, moderate chance of 1 - 2 characters being added)
B Tier
Legend Of Zelda (1 - 3 Levels, low chance of 1 character)
Kirby (2 levels, low chance of 1 character)
Metroid (1 level, High Chance of 1 character)
Fire Emblem (1 level, high chance of a character being added)
C - Tier
Kid Icarus (1 level, moderate chance of 1 character)
F - Zero (1 level, moderate chance of 1 character)
StarFox (1 level, moderate chance of a newcomer being added)
D - Tier
Mother (1 level, low chance of a newcomer being added)
Animal Crossing (1 level, low chance of newcomer addition)
Wario (1 level, low chance of 1 newcomer)
Pikmin (1 level, low chance of a newcomer being added)
Yoshi (1 level, low chance of 1 newcomer)
E - Tier
Game & Watch (1 level, no character)
Ice Climbers (1 level, no character)
F - Tier
Electro Plankton (No level, no character)
Gyromite (No level, no character)