Powder, from any company that you find reputable. I like the micronized form. I would avoid any of the gummies, as a huge percentage of them have nowhere near the amount of creatine they claim (I believe the cooking process denatures it or something but this is just conjecture).
I get mine from bulksupplements. Gummies and many gym focused powders are extremely overpriced. Buying in bulk you should be able to get it for ~$.15 a day at 5g.
Sorry just seeing this. NSF provides their own index. The certification guarantees a label is what it says it is. I don't generally care about branding and let the certification + drug (creatine) do the talking. IIRC evidence points to monohydrate does the job well and no need to fuss with other things like micronized of proprietary creapure.
