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.http://www.guru3d.com/articles_pages/geforce_gt_430_1024mb_review,16.html
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!