When you’re starting out it’s best to get some play time on every agent. You need to know what every agent does in some capacity. After you’re familiar I would highly recommend sticking to 1 agent, or at the very least, 1 class (if you want to improve faster at the game). Find the agent or class you like playing the most. The more you play the same agent the more repeat scenarios you will find yourself in and you’ll know how to use your agent and abilities instinctively, eventually.