With meta, you want to get around his insane horizontal attack range. Full jump bair and nairs hitting him on the head is the way to go. Homing attack is really good against him because of the angle it comes in at. It also has just a bit more priority than metaknight's nair, but you will often trade hits.
Dair goes through his tornado, so try to jump/spring when he gets you inside it. I wouldn't recommend tilting him because trading hits with his Dsmash is definately not worth it. Just play safe in general.
He's easy to KO actually, dies at around 90% from a mid-high uair. You have to look out for his dair when going for those KOs though.
Things to pay close attention to are his Dsmash which is insanely fast, his upB which can mess you up when going to pursue him, the Glide attack which has priority over *everything* (Do not try to intercept meta when he's Gliding. That thing has a massive deceptive hitbox. Just wait for him to land) and his nair, which shouldn't be too much trouble.
IMO, Sonic is one of the characters that can camp against Metaknight effectively due to his speed, as he relies on timing and precision. You should be able to get off a good amound of grabs because most metaknights don't stay in the air too long.
The matchup is still **** in Meta's favor.