Here is the most recent tier list:

Ranking character
#1 meta knight

:p

Tier a ranking character
#2 diddy kong
#3 snake
#4 falco

Tier b ranking character
#5 marth
#6 wario
#7 ice climbers
#8 olimar
#9 pikachu

Tier c ranking character
#10 lucario
#11 king dedede
#12 zero suit samus
#13 mr. Game & watch
#14 toon link

Tier d ranking character
#15 fox
#16 wolf
#17 peach

Tier e ranking character
#18 donkey kong
#19 kirby
#20 r. O. B.
#21 pit
#22 sonic

Tier f ranking character
#23 ike
#24 zelda/sheik
#25 luigi
#26 sheik
#27 ness
#28 yoshi
#29 pokémon trainer

Tier g ranking character
#30 lucas
#31 mario
#32 bowser
#33 samus
#34 captain falcon

Tier h ranking character
#35 link
#36 jigglypuff
#37 zelda
#38 ganondorf