Again, it's about personal choice and a number of factors, including the wine, location, access to wine makers, price point, and who we are tasting with. We like Windy Point for their location overlooking the valley, and often have a picnic on their grounds. Tefft Cellars, Bonair, Two Mountain to name a few. If it's your first time to the Valley, Sagelands is a large producer and good to visit. We like Claar as for some of their wine case specials. Paradisos Del Sol has more of a homey, different feel from the others. Remember in downtown Yakima you can visit Kana and The Washington Wines Tasting Room (they have one in Pike Place Market), a co-op featuring wines from a couple small wineries. Again, just grab a map and go!
FYI, an interesting option that is on my to-do list is wine tasting on horseback: