3th of Antminers = 5kw (by taking 300watts per Antminer) = 31.654BTC (without shipping) = 25.8k $
3th of Neptunes = 2.5kw = 14.6BTC = 12k $
Two times more $$$ and watts for the same hash-power.
There is a really big difference here. You really can't even get a Neptune for at least another several months so why even compare right now?
The winner in the mining game is the one who as the most power efficient machine (or the one with free electricity).
I know Neptune's will be hashing while Antminer's will be turned off because they use to much electricity.