Supergirl Kels recently took a set and then two more games in GF off of Blacktwins (Cloud player), going with Kirby instead of her Sonic.
https://twitter.com/SuperGirlKels/status/934642058815557632
The fact that she opted for Kirby over Sonic against Cloud says a lot about each character, I think.
Cloud has a fantastic neutral. Sonic has either a strong neutral, a smoke and mirrors neutral, or ignores neutral, depending on who you ask. Kirby has a bad neutral, flat-out.
While Sonic is bait and punish, his punishes are rarely severe. He lands one or two hits, and gets back to that aggravating neutral. Kirby has a hard time getting in, but once he's actually there he has some serious combo shenanigans.
Neither Sonic nor Kirby have an advantage over Cloud, but it seems to me that, when it comes to fighting Cloud, a harder punish game is more beneficial than a good neutral. This goes double if your character lacks significant disjointed. Ideally, your character has all the ingredients (Sheik, Bayonetta, maybe Mewtwo), but if not, then the ability to slip in and wreck seems more of an issue for Cloud.