Overall Turion M520 + ATI Mobility Radeon 4200 will perform better in gaming.
Intel HD may have scored higher in benchmarks because of the pull from a faster processor.
In real-world scenario Mobility Radeon 4200 will perform faster.
On a side note: If you are looking at the benchmarks posted in some sites such as Notebookcheck then don't rely on that as most of the scores submitted there are garbage and unoptimized.
FYI, my laptop (Toshiba L555D-S7005) scored 3.5K in 3DMark05, 4K in 3DMark03, 9.5K in 3DMark01.