My 4.0b tier list. I play the game for several hours nearly every week with 2-3 other good players, and I main Random lol. I don't think this game has an "S Tier" like vBrawl did with Meta Knight. While there are some characters that are certainly the cream of the crop; they are all beatable. Since all of the characters are so good, skill and practice factor into matches a lot more in Minus, and I believe the tier list should reflect which characters equally skilled players would have the hardest time losing with. You can also think of it as the characters with the most potential (characters that have the most good elements) going down the list to the characters with the least potential (characters that are perhaps missing one or more good elements that keep them from being better). I'm sure a few of these choices will be surprising to some people, but tier lists are always opinion-based and therefore debatable.
A+ Tier: King Dedede, Lucario
A Tier: Donkey Kong, Falco, Fox, Jigglypuff, Link, Marth, Meta Knight, Olimar, Pikachu, Pit, Wario, Zelda
B+ Tier: Captain Falcon, Charizard, Diddy Kong, Ganondorf, Ivysaur, Kirby, Luigi, Mario, Peach, Pichu, Samus, Sheik, Snake, Sonic, Squirtle, Toon Link, Wolf, Yoshi, Zero Suit Samus
B Tier: Bowser, Ice Climbers, Ike, Lucas, Mr. Game & Watch, Ness, ROB, Roy
*Characters are listed alphabetically for each tier