SF3301 chip does have the best power efficiency in both BTC and LTC mining.

LTC power measurement
Voltage(V)   Frequency(MHz)   Power(W)   HashRate(MHahs)   W/MHash/s
0.8   450   2.18   1.21   1.79
0.9   700   4.34   1.89   2.30

BTC power measurement
Voltage(V)   Frequency(MHz)   FBB(V)   Power(W)   HashRate(GHash)   W/GHash/s
0.6   225   0.0   10.98   36.00   0.31
0.8   625   0.0   53.60   100.00   0.54
0.6   300   +- 0.6   14.88   48.00   0.31
0.8   870   +- 0.6   77.68   139.20   0.56
0.6   450   +- 1.1   23.28   72.00   0.32
0.8   950   +- 1.1   97.28   152.00   0.64