In search of a main that fits my thought process. Recommendations?

I'm looking for helpful suggestions on which champion(s) to really put focus on. I have a quirky thought process that doesn't outright frustrate my teammates but I know don't make me particularly talented either. Champions with a complex kit are very hard for me to keep up with. I do better with champions whose gameplay is slower. This is due to long-term effects of having a brain operation about 15 years ago back in high school. The effect it had on my personality continues to make me feel cautious and calculating. As such, mages are my preferred champion type to play because of the long cooldowns on their abilities. I have time to think of my next move before the abilities refresh. Jungle and ADC are the hardest for me to play because they are much faster and riskier. Top isn't so bad if I only have to hold out till my teammates can come up to help. I don't like supporting because I get bored with it, and there is no appreciation for when I do things right. I have attempted numerous times to practice and enjoy the role, and I always end up hating it by the end of every match.

--The only champion I have ever really done well on is Vel'Koz. It didn't take long at all for me to hit Mastery 7 on him, and I get an S or A grade pretty frequently with him. My success with a few other mages is "meh." --I'm "okay" at ADC and Top. My ADC champion of choice is Cait, but I like a few others, such as Miss Fortune, Jinx, or Ashe. Top I either play Teemo, Garen, or Illaoi. My ability to last-hit is...not lame, but not stellar either. --I completely suck at Jungle. I have practiced and somehow cannot figure out when to gank, like, ever. --I hate supporting. I'm not too bad at it, but I don't find it enjoyable at all. At best, my lane buddy gets fed and carries, for which I get no praise, and at worst both me and my lane buddy feed unwillingly, and I get ALL of the blame. --I had the most fun ever playing as Leona, but since everyone expects her to support, my motivation to play as her is just about nonexistent now. Interestingly enough, I've always wanted to try playing with her in mid just to see how it goes.

So...any suggestions, or should I do my best on who is available and wait for a future update when a new champion gets released that fits my play style?