If I had to choose between great hosts and great apartment, I would choose the first. But imagine if you would not have to make compromise and you could have both hosts and a wonderful place to live. Actually, there is no need to imagine this scenario: simply contact Graciela and Carlos.
I can only reinforce what is already written in previous reviews: Graciela and Carlos are a wonderful couple who will do everything in their power to make your stay as comfortable as possible in their studio(s). As a matter of fact, my impression is that they will gladly run the extra mile in order to help. The apartment is one of the best ones I have ever lived in (and I have lived in many apartments and houses throughout 10 countries of Europe and Asia). I know where I will want to stay next time I come to San Francisco.
To wrap it up, I can wholeheartedly recommend any of their apartments (even though I lived in only one). By having great and caring hosts like Graciela and Carlos, the only thing you need to "worry about" is to enjoy your stay in this wonderful city.