Interesting thread, surprised it remained civil for this long, let's hope it stays that way
Personally if I had to say what I don't want I'd have to say Toad/Captain Toad, Daisy, Bandana Dee (probably to a much lesser degree than the rest), Zero Suit Samus, any character from the more recent Fire Emblems, anyone from Xenoblade 2, Pichu, and Takamaru.
The Toads simply because I just don't like them, they sound annoying and from how much copy-pasting they've gone through any sort of potential connection to them aside from their voices being memed into oblivion. Captain Toad just feels far too similar to break that mold for me personally, even if the moveset video was actually pretty good.
Daisy honestly has nothing going for her for me, the only thing different about her is that she's more "energetic" and has a flower motif.
Bandana Dee, like I mentioned is actually the least "disliked" here I'd say, since I don't really mind the guy all that much, but at the same time there's just something that makes me feel like he shouldn't be in. Can't explain it, could very easily just be an irrational gut instinct, but it's there I guess.
Zero Suit Samus to me just doesn't feel like Samus, like it just doesn't make sense that actively putting herself into a more vulnerable state would actually make her just as powerful as in her suit. The worst part is is that when it was a thing, (much like how Sheik was in Melee), the Zero Suit was more of a one-off thing that you could play as ONCE in Zero Mission when you have to rely on stealth to survive and would be a bonus at the end of the games for doing well. Plus a plasma whip? Where did that even come from?
The Fire Emblem characters one as well as Xenoblade 2 characters one is very much my most biased ones and I know it. I just don't like how "anime" those games are, and I especially hate the sort of "waifu" thing that those games seemed to be encouraging. Maybe it's because I don't understand the games because I was never interested in them in the first place, but at the same time I just can't not hope in my mind that this stuff gets shafted for things I like (yeah that's extremely selfish and I know it, but opinions are opinions, I'm not trying to say this is what should be how Smash 6 is)
Pichu, like many other people said, is just not that original or interesting anymore, if you're going for another Pokemon, make it unique like my dumb guilty pleasure Mon Barbaracle.
Takamaru is just one of those characters I personally don't care for and I think we're fine with the amount of retro characters we have now (here's hoping Ice Climbers return). Nothing more to say really.
Do want to say though that at the end of the day, just my opinions, agree and disagree all you'd like, not here to start a flame war.