Something I have learnt from being in VGC:
1-NEVER trust a site "Best-selling list". It's not a general trend. Numerous times I saw PS3 as #1 for Amazon Best-selling items and 360 was the leader for that week. It means NOTHING!!!!
2- PS4 is selling better than XB1. So, that's part of the anwer. But let's wait for VGC numbers :)