Playground Games get the best ratings atm, but all within the same series. They're untested elsewhere, and reviewers will inevitably get weary of the same series at some point.
Obsidian seem the most reliable; high scores across the board and across multiple IPs.
Ninja Theory is the most interesting imo; more varied genres than Obsidian and willing to take more risks with any potential new IP.
I think so too. We'll see how the second Playground team will perform. Will match the first. Probably The Initiative will also do great games (though not many). And it should be remembered that many of these studies have recently expanded, and access to better tools and larger resources will allow them to create more ambitious productions.