Which is best buy of the TWO.. desperate

The DDR3 card is the better of thse two.

Specify your mobo model, and your PSU model...
And your mobo just have to have a PCie X16 slot to support the graphics card...

And here are few better options...
Just about £8 more than the 9600GT but would perform as good as the 9800GTX+/ GTS 250...
ASUS ATI 4770
http://www.scan.co.uk/Products/512MB-Asus-HD-4770-PCI-E...(x16)-Mem-3200MHz-GDDR5-GPU-750MHz-640-Cores-2xDVI-HDTV-HDCP

But if you still want to buy a 9600, then get this one...It has 96 Stream processors compared to the 9600GT's 64 Stream processors...
http://www.scan.co.uk/Products/15GB-XFX-9600GSO-580MHZ

or the 9800GT for £70 with Free shipping
http://www.ebuyer.com/product/169143