That depends also on your motherboard and where exactly the SATA ports are. There isn't any different functions, only a physical difference! So the right-angle is what it says it is, a right angled connector to the motherboard, the side where it connects to the drive is the same. The main reason you would want to use it is if there is something in the way that is above where the SATA ports are because the standard cables may not work if there are any obstructions. So if you have nothing that will get in the way, then it doesn't matter. If so, then, you may want to go with the right angled cables.
Hope this explains about which one you need to buy!