I'll agree with Jenise vis a vis your own preferences, but even so, I have a few that I might recommend if you can get in. I like nice architecture and some artistry in my wine experience, so...
If you want a more personalized experience and are interested in quite high end (but worth it, imo), I might suggest
Verite, which is a premium Jess Jackson estate witha French wine maker. Wine News actually has an article on the winemaker. Their second label, Archipel, is an amazing value for a California mountain vineyard Cabernet.
They sit you down with a small group, walk you through a tasting, including a comparison with a library wine. It's a lovely small winery in the beautiful Chalk Hill/Alexander Valley area. Alexander Valley is a beautiful, very rural, much less commercialized country cousin to Napa Valley. Plus, after Verite, you can visit the cutesy tourist town of Healdsburg, which has a lovely town square, plenty of yuppie "shoppes" and some great restaurants. Or-Jimtown Store can set you up with a nice gourmet sandwich and all the picnic items you need. A loveley place!
A second recommendation: Del Dotto Cellars and Caves. A small, family owned winery just east of the town of Napa. Cool 19th century stone building and a grotto/cave. I thoroughly enjoyed their peppery Syrah, and they have an amazing Bordeaux Blend. It's a pricy tour ($40), but you can just taste wines, as well, for less money.
For a more commercial winery experience, I found Merrivale quite enjoyable. This is a big, bustling, friendly place-about as far from Verite in feel and experience as you can get. But, you know, it was a lot of fun-full of blousy people with happy "wine smiles" and a competent crew. They have a really cool cask room that you can view from the tasting room floor. They can pour for you a variety of tasting options, including a nice veritcal of their premier (pricey) Bordeaux blend. Very enjoyable place and a good view of the tourist maelstrom that Napa can be
For an example of excellence in negociant wine production, I might recommend Elizabeth Spencer Wines in the heart of Rutherford, CA-across the street from the Beaulieu megacomplex and Rutherford Grill. Delicious savory wines across the board. Not spoofified sweet at all. The tasting room is located in a lovely small brick 19th century post office and is staffed by a very friendly crew. ES is my first "wine club" that I've every joined.
Sullivan Winery (call ahead) offers really fine restrained, delicious red wines in an artistic setting. Good stuff-very friendly crew.
Venge Vineyards (call ahead) has a cool ghost winery located off the beaten path east of Saint Helena. A very nicely done cave system, small family production. friendly, friendly people. I prefer their Merlot and thier Syrah (both tasty) to the estate cab. When I visited last, the winemaker was actually there testing the sugar levels in the fermenting vats.
Finally, if you are interested in some multi-winery tasting rooms, Napa Wine Company in Oakville offers quite a range of boutique wineries and a lovely array of picnic goods across the street at the amazing (but amazingly crowded) Oakville Grocery.
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