Which champion should I force myself to learn?

In my time playing League of Legends I've managed to become proficient with more than a couple champions I once suck with. The best example is Lulu, one of my favorite and best champions now, but a champion I couldn't figure out at all at first. But she's not the only one.

Anyway, in an attempt to solidify my champion pool, I rated every champion in the game out of 4. 4 stars means one of my go-to champs. 3 stars is just a small step below that. 2 stars are champs I can see myself possibly succeeding with but need to play more. And lastly, 1 star signifies the champs that I'm flat out garbage as. This got me to thinking which 1 star champ would be most worth trying to learn for a support main, top secondary like myself.

So, I thought I'd throw the question out to you all. Which of these champions should I try to learn as best I can?

EDIT: For a point of reference, here are my 4 stars: