DDR5 one because the memory is much faster. Having more memory doesn't really help unless you are using resolutions higher than 1080p or have AA cranked up
DDR5 has more bandwidth so it will be faster. Especially when performing things like AA.
If you always have to choose between DDR3 and GDDR5, ALWAYS go for the GDDR5. The only reason anyone should ever buy a GPU with DDR3 memory is if they are on a really tight budget that can't stretch to a GDDR5 card.