If you have free electricity, that will overrun all other factors. Problem is that people usually underestimate how much electricity will get used.
WRONG!!!!!I don't usually color my text , but this time I had to because your statement is so wrong, let me give you a real life example of a recent mining gear , and that is the antminer D3, if you bought a D3 ( 1200w / 17gh) a couple months ago for 300$ like some people did right before the release of SPx36 (4400w/540gh) where difficulty went from about 60-70 to over 160 and price kept only decreasing , the average daily income you would have made would be about 50 cent day.
that's 13$ a month ! say 15$ a month at best case scenario , that is 20 moths to roi , you are not even half way there despite the free power, let alone the fact that you paid 300$ when btc was under 5-6k which means if you simply held
BTC ,your hodlings would now be worth double without having to worry about running a mining gear.
Same thing goes for a lot of other gears, whereby price keeps going down while hashrate (difficulty) keeps going up due to way more efficient gears being introduced, so it's not all sun shine and rainbows for those who have free power.
and hey ! i am talking from personal experience since I do have free power, and I am sure that anyone who has been in the mining business long enough would agree to the fact the free power is not the only factor that determines a good business.
If you have the time, you can check websites like bitinfocharts.com where you can see both price and hashrate on the same chart, do the math and you will see a lot of gears that never ever going to ROI.
Before I end this, i would put two more examples, which are Innosilicon S11 and Antminer A3 , I still remember how on one day the A3 made 9$ and the next morning it became a door stopper that nets 0 profit, not sure how free power would have saved you from a hardfork against your gear.
edit:
I am willing to bet that the fine gentlemen who think mining alts with (GPUs) has faster ROI or less risk than mining btc with mining gears - probably never tried both, there are many facts to point out to how wrong their assumption is, probably too long to fit into a single comment, but if anyone wants to debate based on statistics and numbers , kindly let me know