1/ which 3 or 4 miners on the market give me the most hashing power using 2 kW per hour
2/ filter out the miners that are preorders
3/ of those left, which is the cheapest
Then look at how many 2 kW power points/fuse circuits you have to fill up, and then every month run this little test again and buy the winning miner until your fuse box cannot take another...or your house turns into a blast furnace of heat.
What's weird is that the cyclical nature of ASICs is so shortlived that I'm sure we could see a pattern where certain vendors are more likely to succeed simply based on what hemisphere they are located in. Right now it's summer in the top half and nobody is thinking about adding more heat (sans maybe the Icelandic folk).