You need to think about what experience you and your partner want. Visiting these wineries is an extremely personal preference. You have essentially 4 categories.
No reservations - walk in, tasting for 4 or 6 wines where they run you right through them, one will be their "reserve for $90 that was rated by so and so 93+), stand at a counter, good people watching, walk the grounds, take some great pics for FB or Instagram. Cost $10-20 (V. Sattui, Domaine Carneros, Chandon, Stag's Leap)
Reservations/group - Have to make a reservation although they sometimes can be done day of. Sit you at a private table or area where you are not bumping elbows. Might include a tour. They will pour 4-6 wines one time through. Cost $40-75 (Schramsburg, Frog's Leap, Nickel & Nickel, Far Niente, Phelps, David Arthur etc BTW all these wines are amazing in my opinion)
Private tasting - Need to make in advance. Pull up to locked gate and announce yourself. Maybe at most see one other couple in the distance or leaving. Walk the cave, wine making area, they will pour 3-5 wines however they will let you revisit any of them as much as you want so you end up drinking a lot of really expensive wine. Cost $75-125+. (Italics, Sinegal, Revana, William Cole, Young Inglewood)
Unique experience - Wine blending class, barrel tasting, picnic and ATV ride etc. Cost $75+ (Phelps Insignia Blending, Del Dotto food Pairing, etc)
Do you want to ship a bunch of wine home, are you looking to hit as many as possible, do you want a truly romantic time away that only places like Napa can do. Did you drink a bottle of Mumm after you proposed then you probably want to go there. Or maybe you go up to Ovid and taste $300 bottle of wine and million dollar views etc etc.
Moral of the story is I encourage you to think about what you are looking for. Also not discussed is traffic and crowds. You don't want to be crossing across the valley back and forth or you will waste a lot of time.
I would never go to V. Sattui, but that is b/c I am looking for a much different experience not b/c one is better than the other.