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.
I simply can not help properly without knowing:
2) any OTHER uses (light gaming?)
GPU acceleration in tools like Maya aren't generally very extensive. That's beginning to change with OpenCL starting to ramp up adoption but it will still take a few years. Basically the processing is done by the CPU, or the GPU, or BOTH.
It's likely that the best solution would be an INTEL CPU with HD4000 graphics, but again it's almost impossible to comment without a budget.
There may be better deals than simply what Dell offers. Bestbuy has lots of choices.
Give us the following information and maybe you can get more help:
2) screen size
3) screen resolution (up to 1920x1080)
4) RAM amount
5) other Graphics needs? (light-gaming, Adobe progams etc)
While 4GB of RAM is plenty for most people, if MAY become a bottleneck depending on what you are doing. If in doubt, 6GB or 8GB might be better.