9.8 MR3 is considered to be most stable, and 9.12 MR1 patch 1 is bleeding edge with new features and enhancements, therefore Ruckus will always recommend that you use what is considered to be the most stable release so you get the best experience
Note: All fixes that are in 9.12 MR1 patch 1 are also in 9.8.MR3.