I order them as
Pichu / Ness > Kirby > Bowser
Kirby has the best game vs Sheik and Puff of them, one of the better games vs Peach (maybe the best, not sure), but he's also got no answer to platforms or dash dance as a result of his total lack of everything. His cohesive options are offset by his lack of a real gimmick that circumvents a huge part of gameplay aside from his crouch. I feel that while this should be a better deal in theory, in practice people attack Bowser as opposed to exploiting his awfulness and since Kirby doesn't have a heavy punish, when they misplay on him he's not likely to garner a swing from it in the way that Bowser might. I think this is a terrible reason to rank them as such because I definitely feel that Kirby affords more room for his pilot to be good because of his larger option pool, but Bowser will probably be ranked higher at the end of the day because Chillin fights DJ entirely wrong for 2 matches, wins the set anyway, but last stock must mean Bowser has untapped potential.
Ness moves a lot but he's freaking terrible when you break him down. Pichu has u-throw nair and a dash dance that is somewhat respectable. I feel this is more useful than Ness's better attacks but this is debatable. Lightshielding on the top platform destroys both of them so I can't really argue about macro games and platform camp. Sheik CGs both of them, and neither of them have much business escaping a variety of the top characters' combos. Pichu's weight offsets his great recovery, Ness's recovery is just garbage straight up. Neither have crouch options.
Peach vs Marth rankings are meh. I already posted my thoughts about it. Peach's weak macro game is sucky but she has a really expansive micro game because of her numerous, exploitable, variable options.
I'd rather talk about Sheik and Jigglypuff, or where people feel Doc should be period. Is he high tier or mid? And so forth.