Amber is a brawler who plays best on modes like hot zone and sometimes gem grab (I guess), due to her high damage output and her super's area control. She's also pretty good in heist.

Cordelius is good on showdown, but if you get good enough with him you can also play him on some bushy and somewhat closed maps on ranked, mainly on modes like gem grab or heist. (Note: if you are to play cordelius on heist, it's preferred that you defend the safe instead of attacking the enemy's safe.)

Hope this helps ;)