The tanky ones are the most successful ones I've seen. AP/AD carry build on her works surprisingly well early on, but without any escapes she gets annihilated by assassins/AD casters later on. Tanky AP seems like it would be the way to go.
You really only need to build tanky if your getting focus fired or they have some champs with high mobility that are picking you off. I suggest CDR/AP starting with boots/wand or boots/tear. Upgrade to Ion, then look for your next CDR item being either morellos or Frozen Heart if you need the armor. If going Frozen Heart it might be a good idea to skip tear and go for an early sheen.
The Tear is a great item on sona as it allows you to build the mana and sustain you need to be continuously casting cords, you always want to be ready with a power chord up, and continuously providing mobility and health regen to your team. If you win top, it really allows you to hold point and last until the 5 min mark before you need to return for mana/items.