The best option for you is to go to to either Jaben or Stereo to audition the selection of amp+DAC they have. Bring your own headphone plus your favourite player/laptop along. We can't tell you which one is the best, as we all have different taste.
BTW, I assume that you are talking about portable amp + DAC. The DAC would only be useful if your source is from your computer or laptop. If you are just using a regular mp3 player, then an amp will suffice. Even then, you may find your headphone is good enough without any additional amp.