The "best" version to download depends on your specific hardware, but there are a few landmark releases often used for XP:

: A highly reliable unified driver for both 32-bit and 64-bit systems, offering excellent stability for the HD series.

Since Windows XP is no longer officially supported, the AMD Drivers + Download Center remains the safest starting point. You can manually browse for your specific product to see the latest available legacy driver for XP. AMD Catalyst™ 15.7.1 Driver for Windows® Release Notes