which sentinel do i learn next

and even then you're just sitting on an off angle waiting for people to walk into your crosshair

Sage is pretty fun if you duo with a player that plays molly based agents (eg: viper, kayo, kj, etc), or overall play with a team that provides average/above-average comms and which includes these type of agents. There's a few different ways to play Sage, depending on the map, covering both defensive or aggressive playstyles. It was (somewhat rightly) nerfed a few times, maybe a little too much (no longer can be considered a top quality healer compared to skye for example), but still quite a versatile agent that's slept on sometimes.