GTX 260 is better than GTS 250. GTS 250 is an improved version of9800GT.based on the article you linked above the GTS 250 have same spec with 9800 GTX+meaning that GTS 250 is 9800GTX+. although the 250 have higher clock the compared to 260, the 260 have more SP and higher memory bit. plus the 260 is based on G200 architecture and GTS 250 using old G92 architecture (since the GTS 250 is based on 9800GTX+)
the only con on 260 is it uses more power than 250