When I first picked up league in 2015. I thought I was going to main zed. His kit looked amazing. Then I found out I'm awful with mechanics, so I went a bit more basic, found this wonderful champ called Vladimir with no mechanics! Now I'm a degenerate Shaco main. How about you?
Because I played before Diana came out I can't say the actual answer of Diana for all 3. The first champ in thought I'd main...I think was Amumu? Or Garen. It was a long time ago.