I would go for riser 2 because the voltage regulator much better for the rx470 and rx480
If you are using a other card you can go with riser 1 doesnt matter so much.
Can you explain me why is the riser 2 better for rx470 and rx480 ? I think the difference is that version 2 is using power supply 12V only (you can use independent 12V power supply) and other versions need 12V and 5V. The disadvantage is that linear regulator heating more than other versions, due to higher voltage drop.