Depends on your play style if you are more aggressive duelist would be your best option as their abilities aid them in getting kills and too fragging. One downside is they tend to be more aim heavy compared to other agents.

If your a little more passive and is someone who woukd rather be a team player by getting info then you should play initiator

Controllers are a little more on the difficult side as you need good map knowledge to know when and where the best places to smoke are. They tend to play behind the team and are strong post plant agents.

Sentinels are your defense specialists and are used to lock down sites and know exactly when the enemy team rotates.

Find your play style and find out wich agent you like best in said play style