User blog comment:B214/Question & Answers 5/@comment-26209278-20150417081238/@comment-16281343-20150417085441

Both were created on the same day; January 16, 2012.

Since this wikia has the complete namespace, you can assume that this (highschooldxd) was created first before the other one (dxd.wikia).

Regardless which was created first, this is the main hub for everything DxD.