Hm, this is a tough decision for numbers 2 and 3 for me...
Well, my first is hands-down
Love everything about her. Her playstyle is perfect for me, letting me support my team in several different ways, and, oddly enough for Sona, I feel like I'm really making a difference sometimes (Though that might mainly be because I'm bronze), whether it's saving my allies with a clutch W, or making a getaway/chase with E, or a well-timed ult or Power Chord. Plus, thanks to my burst on my Q+Passive, I can help burst down a squishy or fight back when necessary. There has been a few times where someone tunnels on me, chasing me down for a kill, but I'm able to get my Power Chord up, and quickly turn and burst them down. The hardest part about her for me is definitely just making sure my positioning is good, and she brings joy to me, since support is my best and favorite role.
Second might be
Now let me preface this by saying I am a godawful jungler. I suck at kiting, my ganks are bad, and I can't make quick decisions to save my life. I tried several different junglers, I tried
,
,
,
,
, and
and not one of them clicked with me. Either I felt way too squishy, or that my ganks just weren't good, and wasn't able to do my job well at all. Then I tried jungle Cho'Gath, and I knew he was the jungler for me. I have no problems with my first clear (barring an enemy invade of course, but eh) and once I get my ult I'm not afraid to get in the fight and tank for my allies. Since I can get really tanky, I'm not afraid to go invade the enemy jungle myself either, and my ganks aren't complete trash. I might not play jungle very much, but the Terror of the Void is my go-to in a pinch.
Number 3 would definitely be
I'm not great at most of the things a midlaner needs to know, but I do very much enjoy the feeling of growing ever stronger as the match goes on. Being able to dump damage all over enemies if they don't shut me down as such a thrill. His Final Boss skin makes him even more fun for me to play, as his voice lines are fun, and something about him emphasizes his "infinitely stronger" mechanic.