I got some TrustFire 18650s with my first good light. They're decent, possibly good for the price, but the slightly pricier ones I got from Solarforce are definitely better -- runtime is better even though the stated capacity is less, and they're still holding a charge a year later while a couple of the TrustFires are not. I haven't used the TrustFires in a while.

As for good things from DX: these light holders are fantastic for 18650 lights. I have three of them.