You are asking the wrong question. What are your system specs, power supply brand and model and budget? If you want to get the right GPU you need to ask which one to get, not just pick between two you already selected.
The GT 740 GDDR5 model is very close in price (about 10%) over the DDR3 model, I would go with a 740 GDDR5, but for about that price are some faster cards if you look around. The 750 is about $100, same as the 740, so is the Radeon R7 250X.