Popular opinion seems to think Sandisk is the best for the Nook. I doubt you'll see much difference in Class 4 or Class 10 for general purposes. My Nook color was rooted and running off a class 4 Sandisk and it seened slow at times, but that was probably because everything was running off that card. I got an AmazonBasics class 10 16Gb card for about 20 bucks on Amazon and I can tell the difference on the rooted Nook color but I can't tell any difference just doing basic stuff on the Tablet. You've got to be careful buying a Class 10 as some class 10's seem to run no faster than a class 4 and you're wasting your money paying for some class 10's. I clocked mine and it is running at what a class 10 should run. All in all, I've been happy with the Amazon card.
I have the tablet and I did not root it. I made it capable of side loading and downloaded a couple of file mgt programs. I cannot move anything onto the SD card. It doens't matter where the program came from Amazon or B&N. Astro gave me an option to load programs to the SD card. Lost both of them from the tablet.
the tablet recognizes the card and eve set up folders etc. But I can't get anything to move over to the card.
The advantage of class 10 is higher write speeds. Once something is saved to the SD card there is little advantage. This is a big deal on cameras or when editing video but if you are just accessing data already stored, not so much.
You posted in the Nook Tablet forum so I will answer against that! I am using a Transcend 32gb rated 4 card and it works just fine. I was going to get a 6 or a 10 rated card but after a lot of reviewing it was overkill for this device. A 6 or a 10 is better for cameras which require faster write speeds.