Class 6 or Class 10 for Nikon D3100 DSLR camera?

Would a Class 6 SDHC card be ok or would it be way better with a Class 10?

Matters if you are going to do video or not.

if you are- get the class 10
but if you are going to do mainly pictures, the class 6 should be sufficient

The higher the better.

Well for still frame even in burst mode it shouldn't matter that much. But yeah for video better go high here. Class 10 should do Full HD in the best quality.

I have used a Class 6 SD card with my D3100 and it worked just fine. You would only need a higher class if you want continuous shooting, because with the Class 6 it would stop after 6-8 shots. Video also works perfectly with the Class 6.