I dunno, when playing as Lucario or Pikachu (I have no idea when I suddenly became a Pokemon trainer o.o), Sonic isn't as annoying a match up. Troublesome, sure, but still managable. But I've never felt as powerless when playinig as Jigglypuff than when playing against a skilled Sonic (except against Sheik), even against all the bloody Captain Falcons that are ever present. I know Nair beats his Spin Dash, but he's got so much control over how fast he moves that he doesn't have to rely on just a forward approach, playing probably more tricky than Diddy Kong in my book.
It seems like it's harder for us to wrack up damage on him than it is for him to damage us, and even more so for killing. Rest does not seem like a safe option against someone so speedy like him, and due to his good recovery it takes a while to kill him without. Pound needs to be applied carefully or not be used at all against someone like him, who has no problem punishing any mistake made at all. Her floatiness does help her against the "launched into the air -> Spring Jump -> Axe Kick" combo, but only for so long. I'd initially vote 40-60 Sonic, maybe more... I wouldn't put this match up any better than 50-50, and I feel at least 45-55 Sonic is ... honestly a bit generous, but I'd accept that, given I'm a newb. Maybe Pro-er Jigglypuffs could do much better than me.
On that note, I'm going to try to find videos from Youtube whenever a match up starts, so I can comment on them a bit better. Here are a few I found for Jewpuff vs Sanic.
https://www.youtube.com/watch?v=HAwyQqxryLI
https://www.youtube.com/watch?v=e45u9AwdYBc
https://www.youtube.com/watch?v=pFFRhgSMPxg
(I swear, I didn't pick just ones that had more Sonic wins than Jigglypuff wins. There aren't that many up on Youtube from this year, let alone recently, and I wanted to account for the patches if I could.)
On a random note, I have to ask: Is it me, or are Jigglypuff's throws only there to punish shields? Because it doesn't seem like any of them properly kill... like, ever. Or at least I sure as hell haven't been using them right.