What is the best quality SD card?

I currently use a Strontium 2GB & 4 GB SDHC card. Both are Class4. I bought this for my Nikon camera and the camera manual says to use class 6 for HD video, but I've had no problem with class4 cards. Also, I would also not recommend going for bigger than an 8 GB memory card because there might be chances of loosing data while transferring. As far as prices are concerned, I can only advise you to shop for Strontium memory cards because they sell these memory cards at very low prices as compare to other brands.