choose GDDR5 obviously. however, it depends on your budget, gpu, other parts of your pc.
GDDR5 (there isn't even ddr4 out yet, let alone ddr5) video ram is much better than ddr3/gddr3 because gddr5 has much higher memory bandwidth. all powerful gpus, even most entry level gpus need high bandwidth, that's why they benefit from gddr5.
gddr5 chips are more expensive to produce, so memory vendors charge more for them, which results in higher priced gfx cards.