I'd say 9600GT SLI between those two options.
However, considering I'm finding 9600GT's online for about $80 (USD) each, I'd much rather buy a brand new GTX 260 Core 216 and run a single higher end card myself.
MSI GTX 260 Core 216 $189 - $30 MIR = $159 + Free Far Cry 2 game.http://www.newegg.com/Product/Product.aspx?Item=N82E16814127409
Overall, better performance for about the same price.
Of course, I don't know what you can get the card for in Mexico. I doubt NewEgg.com ships to Mexico, but I could be wrong.
This would also require a decent CPU & PSU to keep up with the demands of the GTX 260 though. So there's a bit more to it than price.