There are several benchmark tools on Google Play Store to benchmark SD card performance. After tried out some of them, I found out that SD Tools and A1 SD Bench provide accurate and consistent data. SD Tools is good but it can’t be used on certain Android devices like Samsung Galaxy S3 and Galaxy Note 2. But it is working fine on Galaxy S4. A1 SD Bench works on every of my Android devices. Besides, it provides the ability to test internal memory, SD card and system RAM too. However, it includes cached data sometime. Therefore, you need to benchmark several times to get the correct result.
Both benchmark tools have almost the same writing speed. However, SD Tools has higher reading speed. So which is the accurate one? Try them out and let me know.