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.