My cake experiences at Miette have been uniformally negative...looks good ...no taste... Perhaps Delessio's on Market, (they really know their chocolate!) or Schubert's on Clement..(old fashioned..whipped or buttercream)
Although they only make one cake, Arizmendi Bakery on 9th between Irving and Judah in the Inner Sunset has a killer and I mean killer chocolate cake. I believe it's $28 for a whole cake. You can stop by there and buy a slice to try before purchasing a whole one.
We did the devils' food cake from Tartine one year, and I kid you not, it weighed about 8 pounds. I love the pastries at Tartine and Elisabeth Prueitt is my goddess, but I have to say Miette knows its cakes. I would do Miette, hands-down.