Morgana is a good and viable AP Mid to learn the role with. She has her counters like any other champion but is good at farming, roaming, and brings a lot to team fights. I really recommend picking her up over Teemo.

Ionic Spark is a pretty terrible item in all cases I've seen for reasons mentioned above; you don't WANT to multi-hit minions, since it invariably winds up pushing, and can often cheat you out of last-hit opportunities by helping your own minions last-hit them. If you want to go with an on-hit Teemo, the three core items you'd almost certainly want are a Wit's End, Malady, and Phage. (though not necessarily in that order)

Meanwhile, on the other side Morgana is a very versatile AP Mid, who in teamfights can, with skilled hands, switch between carrying and supporting pretty seamlessly. However, she does take a bit more skill to use properly; an easy mistake is to over-use her W, which is a surefire way to push too much when you don't want to.

My vote goes to Morgana. While somewhat hard to pick up, especially for a new player, Morgana is a very rewarding champion to play. She has a huge presence in team fights and her laning phase is relatively easy due to her W skill coupled with her passive life steal. Furthermore, Morgana is very viable in ranked where as Teemo is of limited use in the current meta.