I can't be sure if it's the fact that TCM has filled its schedule for fifteen years with Warner Brothers movies -- and so I've simply been inundated with them to the point of brainwash -- but I think Warner Brothers is my favorite of the old time studios.
This opinion was confirmed when I recently read "The Hollywood Studios" by Ethan Mordden. I'm less familiar with Paramount, Universal, and to a lesser extent Columbia (mostly because TCM doesn't always play a lot of movies from these three studios because of rights issues and such and also because the studios themselves release very little onto DVD), so reading about these studios and their movies from the Golden Age has made me eager to find some of these films and explore some new cinematic territory.
But the chapter on Warner Brothers was enough to remind me that even if/when I do see more Paramount or Universal films, they probably won't be enough to dislodge my love for the WB studio.