id say it denpends on how many slots you have on your mobo and if you plan on expanding more in the future. If you have 2 slots and fill them with 2 256 ddr400, pending your mobo can handle it (check the manual), you're not going to have any more room 2 expand. But i think its an advantage to have the 2 separate stick cus if one does fail, which i think is rare, the other stick will still keep your comp alive.
if your motherboard can take it get 512 DDR400 PC3200.
get2 x 256Mb DDR400 PC3200 (512Mb Total) if you have dual mode/ channel enabled and integrated video or if you have dual mode/ channel disabled and no integrated video
Your question was what is the best. If you are planning on staying at a total of 512Mb, then get the 2x256Mb DDR 400 (PC3200). If your budget allows it then you might want to go with two (2) of the 512Mb DDR 400 (PC3200). Make sure that if you purchase two (2) that you put them in to the correct slots so that they will be enabled at the dual mode rate. Yep, it makes a difference.
if I get two of the EXACT same chips....how will switching them around make a difference....actually..the computers bein built and tested for me so..nothin to worry about
Try to get a twin pack of something. They are usually tested together and work most of the time.
On that particular Asus board, you need to put the sticks on the outside and leave the third empty. This will enable the DDR.
Go with PC3200. It's easier to over clock than with PC2700.
And finally, I read a while back that you need to run two sticks of RAM for the AMD cpu's. Intel can run one stick of 512, but with the AMD you should run two 256 sticks or two 512 sticks. Never just one stick.