Doc if your looking to solo clutch, echo if your playing info, clash if you can make good callouts and have some friends to take advantage of those callouts.
Depends on play style,map,rank,teamplay,etc... My top 3 would be. *Echo: He's a really good support op and in the right hands can change a round in your favor. *Mira: She's a solid Support frag op, paired w/ bandit & jäger she becomes almost unstoppable. *maestro: he has very good utility and doesn't need coordination to affect the round.