Hi Linchanlong:
I am sorry but can you please share the Output load current ? Assuming it is between 300mA- 2A for the 12V output, then MP3437 is the best choice for efficiency. The next option is MP1541. The MP3437 has >95% efficiency at 1A when input is 3.4V. The MP1541 has > 85% efficiency when the input is 3.4V for load current between 50-150mA.