Of the two you mentioned (and assuming the 5570 features DDR3 as well) the AMD HD5570 is slightly better depending on which game you use tot test it. Here is a review of the Geforce 430GT which also features results from the 5570.
Sometimes the 5570 is faster, other times the 430GT comes out (a few FPS) ahead. Considering the AMD card is a few bucks cheaper and performance wise there's little real difference, I'd opt for the 5570. Good luck anyway!