Before her health nerf, it was Sona hands down lol. If people wouldn't be so paranoid and rage/dodge I would've taken it to ranked because she was completely viable. I seriously hard-carried games with her. This was back when you could see normal elo and I was about 1650 at the time so it's not like I was just killing complete baddies.
Now...Leblanc ain't bad as someone else said, but she doesn't compare to what AD Sona used to be.
Kennen absolutely. In fact I'd say he is better than AD bot Varus. He doesn't lose lane too easily and actually sort of counters many common champions and strategies. If he had even a small steroid I think he could be a really good AD but even now I'd like to see him getting played more. Especially Runaan's Kennen is something I would like to see.
Jayce. He isn't so bad as an AD he has some issues but also some strengths.