New champ to play
 

So I'm finally ready to settle down and focus on two our three champ. Usually if I have to tank I use mundo because he is such a great counter to a singed. But I'm really open to champs and builds. I really enjoy assassin type champions. Really want suggestions for maybe four champs to focus on. A tank, ad/ap carry, ranged or melee doesn't matter. A support champ maybe. I usually play teemo or sona if I play support. and one more to just have in my arsenal. Suggestions and builds are welcomed.

Tl;dr want suggestions on a few new champs to perhaps stay focusing on I own all except urgot, ezreal, galio, yorrick, and a few others.