Personally I would go for the GDDR4, but some people would just get the GDDR3.
You will get something of a performance boosst from the GDDR4. How much that is I don't know but there will be one.
There really isn't that much of a noticeable difference between a card running GDDR4 and GDDR3. Naturally the GDDR4 is faster, but were only talking maybe a 5% difference.