A: At the moment, versions 2.4 and 2.5 work the best for R5xxx and R6xxx GPUS.
SDK 2.6 or 2.7 works best for R7xxx. SDK 2.8 is known to have many problems.
If you are need to use the 2.6+ SDK or R7xxx or later, the phatk kernel will
perform poorly, while the diablo or my custom modified poclbm kernel are
optimised for it.
Q: Which AMD driver is the best?
A: Unfortunately AMD has a history of having quite a few releases with issues
when it comes to mining, either in terms of breaking mining, increasing CPU
usage or very low hashrates. Only experimentation can tell you for sure, but
some good releases were 11.6, 11.12, 12.4 and 12.8. Note that older cards may
not work with the newer drivers.
I would recommend 12.8 with the included OCL runtime for 7xxx cards.
13.1 is better than 13.4, but neither are particularly amazing, as I believe their OCL Runtimes are based off SDK 2.8.