After saying "**** everybody, I could **** all of you with link", calling people noobs and saying they have no idea about the game, you just go, change characters and act like that's what everyone was advising you to do?
The point wasn't making you change characters.
Sure, some people were saying Link sucked and you would never be good with him, but the rest were telling you to practice, go to tournaments, get experience, and try to get better, no matter what character you were playing.
If you like a character you CAN stick with him and be good.
There are many players that do incredible stuff with mid-low tier characters, so it's not like it's impossible.
Is it easy? No.
Does it take a lot of effort and practice? Sure.
But where you are right now you would have to practice a lot, no matter what character you're playing, if you want to really become good.
So try and reconsider this decision, if you actually have more fun playing with Marth, then go for it and stick with him, but don't act like you had to do it in order to compete.
Experience and skill at the game had more to do with your loss at that tournament than character choice, but I don't blame you, you just got into competitive play and we all have to start somewhere.
Just try not to insult everyone the next time you ask for advice, what they say could be very helpful, if you listened to it instead of dismissing them as "haters".