It's a heated topic, for sure. I'll give my answer and someone will pop in to refute it.

My answer?

You can trusty Butterfly Labs. You can trust the folks at btcfpga.com.

The reason I say this is because I have products from both. Not ASICs, as they've not been released yet, but FPGA devices from them. Any company could decide to up and screw over their customers, but both have proven that they CAN develop and ship a functional product.

Now, what remains to be seen is how well their ASIC products perform once they ship. But I trust that both will ship, and they will be awesome, and they will not screw over their customers.

I would not buy a product from a company that has not yet shipped any product. There might be legit vendors that will produce ASICs, but I wouldn't risk the kind of money on it.