Well, now what Activision-Blizzard is being acquired, I guess I will give a tier list here:
S Tier (top tier studios/teams, their games are well received critically (85+), well received commercially (pretty big sellers), and I personally have played every game they have released in recent years and am interested in playing all future games from them)
- Bethesda Game Studios
- Playground Games
- 343 Industries
- Blizzard team 4 (Overwatch series)
A tier (studios/teams that meet at least 2 of the 3 criteria above or the other, but not all 3)
- The Coalition
- id Software
- MachineGames
- Arkane Lyon
- Arkane Austin
- Tango Gameworks
- Turn 10
- Blizzard Team 1 (Starcaft series, Heroes of the Storm, Warcraft 3 Reforged)
- Blizzard team 2 (WoW)
- Blizzard team 3 (Diablo series)
- Blizzard team 5 (Hearthstone)
- Obsidian Entertainment
- Infinity Ward
B tier (studios/teams that meet 1 of the criteria above, but not 2)
- inXile
- Treyarch
- Sledgehammer Games
- Rare Ltd.
- Mojang
- Double Fine
- Undead Labs
- Zenimax Online Studios
C tier studios (studios that fail to meet any of the 3 above criteria currently, but I see S, A, or B tier potential for in the future)
- The Initiative
- Compulsion Games
- Roundhouse Studios
D tier (support studios currently, though there is potential to go higher for some of them in the future, based on past experience)
- Beenox
- Toys For Bob
- Demonware
- High Moon Studios
- Alpha Dog Games
F tier (studios I have no interest in whatsoever, mobile developers)
- King
- Digital Legends Entertainment
- Alpha Dog Games
- Solid State
