S Tier-
1. Falco
2. Fox
3. Marth
4. Sheik
5. Captain Falcon
6. Peach
7. Ice Climbers
8. Jigglypuff
A Tier-
9. Samus
10. Dr. Mario
11. Mario
12. Luigi
13. Pikachu
14. Ganondorf
B Tier-
15. Yoshi
16. Link
17. Young Link
18. Donkey Kong
19. Mewtwo
20. Mr. Game & Watch
21. Zelda
F Tier
22. Ness
23. Roy
24. Kirby
25. Pichu
26. Bowser
My reasons for Falco being #1 is the fact that he has some areas where he's actually better than Fox. While his attacks aren't as quick and his recovery is poor, Falco has incredible power and combo ability, and his down aerial spike is one of the best moves in the game.
Mario is a character who I think is underrated. Sure, he lacks a reliable finisher outside of his side smash, but his combo ability is superb and is easy to rack up damage with. Also, he is a character that is very easy to master, unlike other characters. Not to mention, his cape is one of the best edgeguarding tools in the game.
Now, about the bottom tier: Roy is ranked in the bottom due to his significant flaws of killing and surviving, which leads to awful matchups. For god's sake, he loses to Kirby.
Kirby was severely nerfed, but he isn't at the bottom because he does have positive matchups. Very few, but they do exist.
Pichu has the worst matchup spread in the game by far. He's the easiest character in the game to kill, he hurts himself, and is surprisingly easy to chain throw. He has strengths, but they literally do nothing to help him. Yet, he's not the worst.
Bowser is definetly the worst character in the game. His approach is worse than Kirby's, he's literal combo food, he has a horrendous SHFFL and wavedash, an ineffictive projectile in his fire breath, his recovery is slow and painfully easy to edgeguard.... He's just the worst.