So we've talked about chocolate tea before. I've liked it in the past, including at Physical Graffitea, which is a truly lovely establishment on St. Marks.
That said, I do recommend the Florentine tea over the Chocolate or Chocolate Chai. Neither of the latter two were sufficiently chocolatey -- which surprised me, given how good the Florentine was (and that was chocolate-hazelnut!). Honestly, with or without sugar, it was hard to detect much chocolate flavor at all.
Bottom Line: A really great tea shop, but if you want a chocolatey tea, stick with the Florentine.