You asked me which graphics card is better, so I'd say HD5450. Currently, a dual-core is sufficient for optimal performance, as not every game takes advantage of all four cores. If you want to be able to play more games without upgrading the graphics, try the Athlon II X2.
If you wish get a better graphics card in the future (or now), buy the one with the Athlon II 640, since it''s faster in almost every single way, though, you can do better with the processor, perhaps buy one with Sandy Bridge or Phenom II?
A decent graphics card would be HD5770 or the GTX 460 SE for only $110 and $150 respectively.