There's a distinction to be made between Bethesda Game Studios (who developed Fallout 3 and the Elder Scrolls games, not including Elder Scrolls online) and Bethesda Softworks, who publish games made by development houses that are subsidiaries of the parent company (e.g. RAGE is made by ID Software, Evil Within is being developed by Tango etc.). They all answer to the same boss if you go far enough up the line, but in terms of creative credit, most people would usually go with the developer in my mind. Publishers can vary across time and region; Doom 3 was originally published by Activision and the later BFG edition was published by Bethesda after their company acquired the developer, but it's still just an ID Software game in my mind.
I've probably put more time in to Bethesda games in total. Gotta give Valve credit for Steam though, which has been a big boost to PC gaming.
I like Valve, Steam works fllawlessly, and they even let you add some games you didnt even buy from them to the library. But WHY are they taking so bloody long with half life 3? If another 5 years go by before we see it, I'm going to get pissed.