Alright brehs, tell me four characters, one in each class, that I should 'main'. So far I've got Pharah for Offense, and maybe Lucio for healer. The other two though? Just want one solid champ in each class for ranked play.
You shouldn't just "main" 4 characters IMO. There are certain characters that excel in Assault and others for Defense. You should have a couple in each class.
For instance, when playing on assault side, if I play offense class, I'll pick up Tracer because she can push up really quickly, and get behind enemy lines easily. She can creep up behind a Hanzo or Widowmaker easily and kill them off with her guns, or blow up a bastion/tjorborn turret with a sticky bomb, which can help open up a push. Whereas on defense, she's not as useful in that regard because you need to keep a team pushed back. That's where I'll pick up Pharah. She can concussion blast people in certain directions, has long-range attacking to keep enemy lines pushed back, and a really good ultimate for clearing a push/contested site or payload.
Plus if one of your assaults isn't working out, but you still need offense damage, you should be able to pick up another character.
Symmetra is another really good example. She's absolutely useless on the 1st half of assault side on a map like...say...
Hanamura...since you usually have a short distance you need to push in order to capture the site. Her teleporter isn't really necessary, she's not really healing, and her turrets are more defensive than offensive. But on the 2nd half of assault side on Hanamura...her teleporter is much more useful since there's a longer distance to cover getting to that site but her turrets, not so much, unless you're facing an aggressive team.
Basically your pick should consider the map/side you're playing and what you'll be doing for the team. A lot of hero's are good on both sides of the maps, but there are usually some that are better suited for certain tasks. If you're defending, you don't need a diving dikkhead like Winston as much as you want a character than can isolate a team like Roadhogg.
You can obviously still have players you fukk with more than the rest(I'm a Mei, Tracer, Lucio guy myself) but you want to be able to adapt to the other team as well, and making changes is a huge part of that.