Overwatch Hero Selector helps you select the right Overwatch hero based on your teams comp and the enemy teams comp. The app will work with as much information as you provide and does not need enemy team information to give a recommendation. Enemy team information is helpful to help pick counters but of-course players will not have this information at the start of a match.
Overwatch Hero Selector assumes that a player is proficient with all heroes. Please dont pick a hero that you are unfamiliar with because the app said it was the best pick.
The app prioritizes the following:
Heroes in the current meta
Heroes that are easier to play
Healers have top priority(if your team doesnt have a healer, the app will tell you to pick a healer)
Tanks have second priority (if your team doesnt have a tank but has a healer, the app will tell you to pick a tank)
DPS are picked depending on the current meta and the composition of the enemy team.