7 vs. 6a are in all essence very similar phones and it all boils down to how important a better screen, a slightly faster and more efficient processor and a better camera with "ultra wide" sensor is to you and if it justifies the doubling in price.
I went with the 7 but the 6a is a very good phone too and the camera is actually still pretty good despite being a slightly old sensor.
I would go to a store where you can try both phones before you make your decision.