best Colosseum team?

Check out BitDynasty's channel on YouTube. He has a lot of videos on getting better scores in the Coliseum. 

I like to use Jedi Knight Cal Kestis (Leader), Jedi Knight Luke Skywalker, Mace Windu, Kit Fisto, and Mara Jade Skywalker... it has worked the best for me.

go to holotables.xyz enter your ally code and see the best teams (note that the teams are submitted by players so you might get a different score)

Same, but on bosses that counter attacks work on JKL can be a better lead because of his Jedi's Will Counter mechanic.

Then again the best thing is getting RNG in your favour mostly for high scores!

Kit fisto is useless. Neither big dmg not debuffs. Jkl, jkck, mjs  and then rest depends on what boss you are facing which can change between cls, qira, chewpio or mace.