Class 4 is what comes standard in the phones. Honestly you will not notice a difference in the classes unless you're transferring files between the phone and a computer. If you're looking for increased speed on how the phone reads the files off of the card... you will not even notice it. Only when transferring files on/off the card will you see a speed improvement. So unless you constantly transfer large files from your computer onto the phone... I would stick with a class 4 for the money. Just make sure you stick with known namebrands... there's a lot of cheap 32G cards on eBay that are knockoffs.