Help! Should I buy Leblanc or Kassadin? Who is more fun and easy?

....both are very difficult to play. I think LeBlanc is more fun personally. Kassadin isn't as much of a burst assassin so much as a highly mobile off-tank mage/fighter

Talon, Akali, and Katarina are easier to pick up

Ahri is a pretty easy champion to pick up with lots of potential. After lvl 6+ dfg you can roam bot.

Zed. Easy early and late, and getting kills doesn't require as much skill as people seem to think. You can also pull off some fancy jukes once you get better with him.