I refuse to rate the roster with the Grinch leak for now, making a final judgment call against the other rosters is just unfair if I'm taking that leak into account (A. Because it would win without a doubt B. If I do that I feel like I'm condemning the leak for certain at that point haha/I'm still leaning towards it being fake).
1. Brawl - Just objectively has the best newcomers. So many big names in that game that deserved it. Wario, Diddy Kong, King Dedede, Meta Knight, and Pokemon Trainer were all pretty massive additions. I loved the smaller, less known choices as well such as Ike, Olimar (Even if I still suck trying to play as him), Wolf, and R.O.B. especially. Also, getting the first third party characters ever was amazing, especially when one of them was Snake and Sonic was coming in to the Nintendo home front essentially. I know some people were disappointed, but that really had to have read like a dream roster at the time.
2. Smash 4 - For as much flack as I give Smash 4 and the roster choices, I will say many of them were inspired and contributed good characters to the game. Shulk, Little Mac, Mega Man, Duck Hunt, Villager, and Mega Man are all additions I absolutely adore and can't do without now. Fire Emblem needed a different kind of character and Robin was just that (Still to me the most inspired FE character). Bowser Jr. and Wii Fit Trainer are weirder characters I had no interest in til I saw them in action. Greninja accidentally became my second favorite Pokemon in the series. Rosalina played very unique and I was happy to have her. Palutena made sense though I wasn't a huge fan. The only characters I wasn't keen on were Dark Pit and the Mii Fighters, which holds true to this day. Add in DLC and this game becomes even better.
3. Ultimate - I mean Ridley and King K. Rool have been my number one and two since Smash 4. Castlevania is one of my favorite video game series, and I couldn't ask for better representation in Smash. Inkling is the most sensible and well done addition of this game I would argue. Isabelle is adorable and I think Animal Crossing deserved a second representative. Dark Samus is the best kind of Echo. Only Chrom and Daisy do nothing for me, and I at least see why they were added.
4. Melee - Yay, I'm continuing the trend of everyone else. Melee had some great additions. Boswer, Peach, and Zelda were all necessary additions at that point. Shiek, Marth, and Mewtwo were great additions, and we got our first taste of weird in the series with Mr. Game and Watch and Ice Climbers. All the unique characters were pretty good. Though, not necessarily my personal favorites of the series. The over reliance of clones such as the poor old Ganondorf, alongside the likes of Young Link, Pichu, Roy, and Dr. Mario all felt weird though. When Ganondorf gets that poorly represented, and the remainder on the clones are strange choices for the time, I'm inclined to give this game the last position on the list.