Dogie's Comprehensive Manufacturer Trustworthiness GuideThe single most important factor when choosing an ASIC is to find a company that will actually deliver you a product. There are too many companies that will happily take your money and basically "never" deliver.
They either literally never deliver (outright scam), or they deliver so late that by the time you get your ASIC it will only be useful as a door-stop or space heater (vapourware pre-orders).
Spondoolies-Tech and Bitmain are my favorites at the moment. The Spond SP10 and Bitmain S1 & S2 all are real products that are delivered promptly (roughly 1 week).