I'd go with Hercules.
I've had very good experiences with their tech support, and their 2D is better then that of the Asus card.... though neither are by any means great. Also, in my experience Hercules cards tend to be very solid and reliable.
I'm not entirely sure what RAM is utilized on the Asus card is, but Hercules model uses 4ns DDR SDRAM which should in theory be good for 500MHz.