Is there a best character?

yes there is a best character

it's fox/marth

and it's not just opinion, it's basically been proven nowadays

the sad truth is that not all characters are made equal, even if the intention was to have made them equally.

Wait, why Marth and not Roy? Like, what's their difference?

marth's range is much more useful than roy. roy is stronger at the middle of his blade so he cannot abuse his range as much, whereas marth is best at the tip of his sword. this doesn't seem to mean a lot but it makes roy have a much harder time killing people, especially since his air game is so weak compared to marth. almost all of roy's moves are slower, but marth's sweetspot (tip of his sword) is actually stronger than roy's sweetspot (middle of his sword). marth is also faster than roy both in his movement speed and his attack speed.

marth's non-sweetspot attacks (ones where he hits with the middle of his blade) actually have some utility, whereas Roy's non-sweetspot attacks (tip of his blade) are basically worthless. Roy's air game is also incredibly bad, but Marth's air attacks are some of the best ones in the game. marth also has an easier time recovering back onto the stage, whereas roy sort of sucks at that.

what is probably the biggest difference is the fact that marth's sweetspot at the tip means he can control the enemy a lot better than roy can. marth's moves also carry a number of amazing properties (up tilt juggles incredibly well on Fox, down tilt is an amazing edgeguard move, down air is an incredible combo ender, forward air can singlehandedly beat a lot of characters, his grabs have better followups given his sweetspot), whereas roy's moves aren't particularly useful.

thats the gist of it.

Melee Tier list.

Top
Fox 9.88
Marth 9.85
Sheik 9.69
Falco 9.15

High
Peach 8.35
Captain Falcon 8.00
Jigglypuff 8.00
Ice Climbers 7.88

Middle
Samus 6.77
Dr. Mario 6.23
Ganondorf 6.04
Luigi 5.81
Donkey Kong 5.38
Mario 5.34

Low
Link 4.69
Pikachu 4.31
Young Link 4.15
Roy 3.60
Zelda 3.04
Game and Watch 3.00

Bottom
Ness 2.50
Yoshi 2.46
Bowser 2.17
Mewtwo 1.77
Kirby 1.50
Pichu 1.15

Sheik's downB is the worst move in the game.

Yes, there is. It's been proven using the official Tier list. Of course, it's going to be forever argued over.

not too often anymore, since it is not really played competitvely anymore
there isn't any real new data to put in the game