If your time in the Western Cape is short and you are “forced” to only visit one wine farm, then it must be Babylonstoren. The farm is one of the oldest Cape Dutch farms and you will fall in love with all of the sights and sounds that this beautiful place has to offer. Whilst I have never stayed in the hotel or had a chance to eat at Babel or head to the spa for a treatment, I would stongly recommend you investigate this option if you need to book accomodation as I have heard only good things.
But the farm also makes for a perfect day visit where you get to walk the extensive fruit and vegetable garden, enjoy the bounty of its produce at The Greenhouse restaurant and shop up a storm in the bakery, deli and farm store. And you may want to check out their workshops and I just spotted something new: “Tea Rituals”! (a plan for later this year, no?).