I'm not sure whether you mean you never drink Napa or Sonoma county wines, or you drink only Napa and Sonoma county wines.
Robert Mondavi, Raymond and Christian Brothers, of course, are all Napa-based wineries, and their premium wines are all Napa country wines.
Sonoma county wines were traditionally less refined than their Napa cousins, lacking a region with the panache of the Rutherford Bench. Historically, Simi (long lived reds) and Korbel (method champagnois sparkling wine, mostly from grapes other than chardonnay traditionally) made some of the best wines in Sonoma county, with Hanzell coming in with amazing burgundian style wines in the late '50s. And Napa based Louis Martini's famous vinyard that produced the guts of his special selection cabernets is in the hills between Sonoma and Napa county and, if I recall correctly (it's been years since I was up at that vinyard), actually straddles the county line. The great, very long lived, Lytton Springs Zinfandels made by Ridge of course come from the Dry Creek valley in Sonoma county, and Clos du Bois had made some lovely wines in the past 30 years. More recent great Sonoma wineries have included Chateau St. Jean (amazing Chardonnay) and Matanzas Creek (their '85 is the ONLY merlot I have ever bought cases of for aging). There are several old Italian family owned wineries in the Healdsburg area, such as Parducci and Pedroncelli, whose wines have improved greatly over the years, but continue to lack real sophistication. I thought they were more fun when you could bring your own gallon jug and fill up with dago red (e.g. ususally a zin/carignane blend) for $1.50. When I had to spend real money (like $1.50 a fifth or more), I'd go see Isabelle Haigh, the old Simi daughter who was a friend of my grandfather and great uncles. She'd sell me a case of 'carignane' for $12, and it would have 6 bottles of carignane and 6 bottles of the 1935 cabernet savignon. (The '35 was a prize-winning wine, and, for some reason no one remembered, several thousand bottles were bricked up in the undeground cellars and forgotten about until somewhere around 1960. When found, it was amazingly good, and they were selling it (limit 3 bottles) at the winerey for a number of years. I think the last of it was going for some $35 a bottle around 1972.) Ah, memories.