S Tier - Cypher, Breach, Omen
Breach received a major buff in patch 1.07 increasing his effectiveness as an initiator, Cypher also continues to be a must-have in terms of info gathering.
A Tier - Killjoy, Viper, Brimstone, Sage, Phoenix, Raze, Jett
Viper received some major buff to add to her utility in Patch 1.07. Her abilities have been made much better for her team and with the heavy nerfs to Sage, her ability to control enemies will likely let her see some more frequent play.
Let's address the elephant in the room, Sage got nerfed hard. her healing isn't nearly as good as it used to be and her defensive capabilities have been brought way down but, she still is the only Agent able to heal others, so that keeps her up in A tier.
B Tier - Sova and Reyna
Both Sova and Reyna can be highly effective when played right, but their abilities could use a bit of retooling. Reyna's reliance on kills can make her either a beast or a paper cut out, depending on the match and Sova still has a hard time competing with Cypher for the prime info gatherer spot, especially given the nerfs to his arrow bounces.