The Radeon 6620G with 1333MHz memory is almost twice as fast as the HD 3000 for gaming performance, maybe more depending on the game. For non-gming, it's still faster, but graphics performance doesn't make as much of a difference except in GPGPU work as other things. Multimedia should work fine on both graphics, but the 6620G might be a little better.
However, the HD 6620G is only available on laptops with an AMD Llano A6 APU. The i3s can't have it because it is a part of the Llano A6 APU. An i3 could support a discrete Radeon graphics card, but that would depend on the laptop's graphics support.