easy..
what to mine? BTC
how? well if you TRULY arent paying any electricity costs, then you should buy the cheapest old miners out there like some BFL or Avalon G1 old scrap.. this will maximize your Ghz output per $ invested.
after a quick look on the market, I am pretty sure there are many desperate sellers who want to get rid of their old miners for really dirt cheap.
a hash is a hash whether it comes from an S1, A1 coincraft, or a KnC miner..
So do you mean those who pay for electric bil are not having that much profit?
I'm trying to illustrate a point.. which is that if electricity is free, then buy the cheapest hash per $ paid..
for example, if you have free gas, would you factor in MPG in your car buying decision?
same concept applies with miners, if I have free electricity, then I'd buy a cheap-ass 200 Ghz avalon miner (from some1 that desperately wants to sell it) that costs say $200 than say an S1 antminer at $470 or a 200 Ghz BitFury at $800