https://thewirecutter.com/reviews/best-sd-card/After 15 hours of research and another 15 hours of testing, we determined that the 32 GB SanDisk Extreme Plus is the best SD card for most people because it’s reasonably priced and it comes with a lifetime warranty. Oh, and it ended up being the fastest of all the ones we tested after our burst shooting, file transfer, and benchmark tests.
I am using SanDisk Extreme Pro (UHS-I, max 95 MB/sec read, max 90 MB/sec write) cards on my D5100 because i'm planning to upgrade to D7100... and at the moment i have the impression that the card is faster than the camera! That's how i like it.
But less would do as well. Buying a SanDisk Extreme Plus (max 80 MB/sec read, max 60 MB/sec write) confident that it will be faster than the camera as well. Although in the end the writing capability cannot be fast enough (to clear the buffer asap, is my idea), so i will be using the Extreme Pro.
Interesting link: Nikon D5100 Performance (imaging-resource.com)