Good champions?

I just recently got fizz and katarina, they're so fun to play with! and OP as fuaarr. Im nearing 6300 and was thinking about getting, jayce, darius, kha'zix and ahri. Please let me know who i should pick for my next champion, it doesn't have to be a 6300 champ or anyone i just mentioned. Thanks

Darius is really strong top lane, you can never go wrong with dunking kids left and right.