Best 6300 Champions

That's a loaded question. A lot comes down to personal taste and which champs you already have. Lucian is personally the only 6300 ADC I like though Kalista is a good pick, I just don't enjoy her mechanics. For Mid (Mages) Syndra is my go to pick as I feel like she can bring quite a lot to fights as well as quick single target picks and a bit of utility. By no means though limit yourself to 6300 picks though unless you more or less have all the cheaper good champions too.

varus

though technically his price just dropped to 4800 after jhin came out.

mid he can go heavy AD with cdr and armor pen, makes his Q his pretty hard and with cdr he can use it often.

bot he's a regular acd with some CC and can fight tanks well with his W.

As soon as you say "Best" it will come down to some major things:

1. Player's opinion of that champion.
2. Difficulty of said champion.

• Skill floor VS Skill ceiling is what I mean.

is a 6300 IP champion that is relatively speaking easy to learn. While (also 6300 IP) is WAY more difficult, but extremely rewarding once you learn his in and outs (combos, when to use certain abilities, etc).