It's hard to know what is the best type of memory card to buy for your expensive digital devices. Photographers may get confused because there are two commonly used cards for cameras: SD cards and CF memory cards. CF memory cards are used by most DSLR cameras, and they are considered to be the most reliable. If you have spare SD cards and you want to use them, you can simply put them in a CF memory card adapter. Memory cards are rated by class. The best CF memory cards will have a rating up to 10, but a 4 is good enough for most uses.