These are just for fun, or at least something resembling fun.
Statistics could only be based on as many detailed match results as were provided.
The Loyalists! Sticking to one character only:
Aladuf23 (Pikachu)
armubaba (Snake)
Auron_Kale (Snake)
Baiano19 (Zero Suit Samus)
Beezy (Lucas)
bigmakstudios (Pit)
Blizzard (Kirby)
Bloodwake (Captain Falcon)
BlueSummers (Ness)
bran (Marth)
Costanza (Kirby)
Crimmy (Snake)
DeceitDecide (Pikachu)
Dragmire ("Zelda/Sheik")
funkmastergeneral (Pikachu)
Gamer @ Heart (Kirby)
JSnake (Ike)
justchris (Kirby)
Kinosen (Diddy Kong)
layzie1989 (Lucas)
Malfunky (Snake)
Masked Man (Lucas)
MGrant (Ness)
Michan (Mario)
MrCheez (Olimar)
NeoForte (Lucas)
OliveJuice (Falco)
PillowKnight (Marth)
PunjabiPlaya (Ike)
Rentahamster (R.O.B.)
RevenantKioku (Jigglypuff)
Schattenjagger (Link)
scottnak (Kirby)
shaft (Ike)
Shanks (Ike)
SS4Gogita (Lucas)
Teasel (Olimar)
Toy Soldier (Pokemon Trainer)
TwinIonEngines (Peach)
WalkMan (Luigi)
XiaNaphyrz (Zelda)
Zozz (Diddy Kong)
Two-Timers! Using two characters:
Acerac (Kirby, Lucas)
biggkidd32 (Lucas, Wolf)
BudokaiMR2 (Marth, Toon Link)
crowphoenix (Ike, Toon Link)
dfyb (King Dedede, Ness)
dragonlife29 (Jigglypuff, Yoshi)
Dreavus (Ganondorf, Meta Knight)
Einherjar (Ganondorf, Ike)
Fenix (Captain Falcon, Ike)
Firestorm (Meta Knight, Toon Link)
Hatchet Man (Lucario, Mr. Game & Watch)
HotByCold (Kirby, R.O.B.)
ICallItFutile (Marth, Toon Link)
infiniteloop (Mario, Meta Knight)
JoeFu (Mr. Game & Watch, Pikachu)
KevinCow (Mr. Game & Watch, Olimar)
kIdMuScLe (Ike, Marth)
Kusagari (Diddy Kong, Lucas)
Kwokuen (Marth, Wolf)
Milabrega (Mr. Game & Watch, Pit)
muttyeah416 (Diddy Kong, Marth)
Phantom Flapjack (Ness, Zelda)
projectkuro (Mr. Game & Watch, Wolf)
Relix (Luigi, Toon Link)
rhfb (Olimar, R.O.B.)
SixStringPsycho (Fox, Ike)
Spruchy (Ike, Marth)
superbank (Captain Falcon, Ness)
truendo (Samus, Wolf)
usea (Olimar, R.O.B.)
Vanish (Olimar, Snake)
vertopci (Falco, Fox)
viewtiful_dru (Lucas, Pikachu)
weepy (Diddy Kong, Kirby)
yeb (Meta Knight, Snake)
Zeed (Lucario, Marth)
Trinitarians! Playing three characters:
Arol (Lucario, Meta Knight, Toon Link)
Cowie (Diddy Kong, Olimar, Toon Link)
Crushed (Marth, Snake, Wolf)
Cyan (Diddy Kong, Kirby, Pikachu)
Dechaios (Diddy Kong, Ganondorf, Wolf)
Dr.Hadji (Falco, King Dedede, Kirby)
Economan (Bowser, Ness, Toon Link)
Enk (Kirby, Link, Pit)
Guled (Bowser, Lucas, Snake)
Iam Canadian (Lucas, R.O.B., Wolf)
JCX9 (Marth, Pikachu, Pokemon Trainer)
Keru_Shiri (Falco, Ike, Pikachu)
LouieGeetoo (Ice Climbers, Pikachu, Wario)
Manabanana (King Dedede, Lucas, Sonic)
Mark D (Diddy Kong, Meta Knight, Toon Link)
slayn (Ike, King Dedede, R.O.B.)
tmdorsey (Marth, Peach, Toon Link)
Vlad (Pit, Sheik, Sonic)
Adventurous Souls! Playing four characters:
Killa Sasa (Donkey Kong, Link, Mario, Yoshi)
miggsthejust (Ike, Meta Knight, R.O.B., Wario)
Jacks of All Trades! Playing five characters:
jibblypop (Fox, Ike, Marth, Meta Knight, Wolf)
Nabster92 (Captain Falcon, Ike, Marth, R.O.B., Zelda)
SuperAndroid17 (Ike, Link, Mr. Game & Watch, Wario, Wolf)
Teknoman (Diddy Kong, King Dedede, Lucario, Pokemon Trainer, Snake)
Variety King! Employing six characters:
Halycon (Ike, Lucario, Olimar, Pit, "Zelda/Sheik," Zero Suit Samus)
Master of Double Digits! This person called upon ten characters--ten!
Jiggy37 (Ice Climbers, King Dedede, Kirby, Lucas, Luigi, Marth, Mr. Game & Watch, Pikachu, R.O.B., Zelda)
*********************************
One-night stands! Never playing a character more than once:
Einherjar (Ganondorf, Ike)
JoeFu (Mr. Game & Watch, Pikachu)
HotByCold (Kirby, R.O.B.)
usea (Olimar, R.O.B.)
Do you have ADD? Never playing a character more than once... Despite participating in ten matches...
Jiggy37 (Ice Climbers, King Dedede, Kirby, Lucas, Luigi, Marth, Mr. Game & Watch, Pikachu, R.O.B., Zelda)
Stick to it! Playing a character between five and nine times:
Aladuf23 - Pikachu x5
Arol - Lucario x9
Beezy - Lucas x7
Blizzard - Kirby x7
Bloodwake - Captain Falcon x7
bran - Marth x6
BudokaiMR2 - Marth x9
Cowie - Toon Link x8
Cyan - Pikachu x8
DeceitDecide - Pikachu x7
Dechaios - Ganondorf x6
Dr.Hadji - King Dededex9
dragonlife29 - Jigglypuff x6
Enk - Kirby x5
funkmastergeneral - Pikachu at least 8 times
Iam Canadian - Lucas x7
JSnake - Ike x5
Keru_Shiri - Ike x5
Killa Sasa - Donkey Kong x7
Kinosen - Diddy Kong x7
Manabanana - Lucas x6
Masked Man - Lucas x7
Michan - Mario x5
miggsthejust - R.O.B. x5
Milabrega - Mr. Game & Watch x6, Pit x7
Nabster92 - Marth x7
Phantom Flapjack - Ness x6
Rentahamster - R.O.B. x7
scottnak - Kirby x7
shaft - Ike x7
slayn - R.O.B. x5
Spruchy - Ike x7
SS4Gogita - Lucas x5
SuperAndroid17 - Wolf x8
Teasel - Olimar x9
Toy Soldier - Pokemon Trainer x6
viewtiful_dru - Pikachu x5
weepy - Kirby x5
Zeed - Lucario x6
Zozz - Diddy Kong x5
Run with the ball! Playing a character between ten and fourteen times:
Arol - Toon Link x10
Dreavus - Meta Knight x10
Iam Canadian - R.O.B. x14
Kwokuen - Marth x10
MrCheez - Olimar x13
OliveJuice - Falco x14
PunjabiPlaya - Ike x10
XiaNaphyrz - Zelda x10
Such dedication and success! Playing a character between fifteen and nineteen times:
biggkidd32 - Wolf x15
BlueSummers - Ness x15
layzie1989 - Lucas x15
Testing the upper limits of skill! Playing a character between twenty and twenty-four times:
Crimmy - Snake x20 (at least)
Relix - Luigi x20
yeb - Snake x21