Q: What makes a Hero high tier?
A: Heroes that I rate highly do extremely well in several of the following categories: map control, objective control, waveclear, burst damage, sustained damage, poke, ganking, survivability, and factor X (unique strength). For example, Kael’thas deals extremely high area of effect damage (sustained and burst), has excellent CC, some of the best waveclear in the game, self heals, can insta-kill an enemy, and is strong at all points in the game. His main weakness is his lack of mobility and fragility.
Q: What does it mean for Hero to be a higher tier?
I’ve defined my Tier List as what Heroes I think are most effective at carrying games. A higher rated Hero will be able to carry a game much more easily than a lower rated one. However, this is not always true, there are a lot of factors that go into making a Hero the “right pick” for your team. For example, you may not want to pick Li-Ming versus a team encompassing Zeratul, Tracer, and Illidan, and instead opt to pick Sonya. You should always select a TIER S Hero if they are available though.
Q: Would I ever pick a TIER 2 Hero over a TIER 1 Hero (if both options are available)?
Yes. Some Heroes are extremely good on some maps or with or against specific Heroes. For example, Sonya is a much better choice than Thrall on Infernal Shrines if your team has a Tassadar and a Rehgar (making it very difficult for the enemy team to kill Sonya). You should generally pick the Hero that you are more comfortable on as well.
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