I'm quite happy with my Rev B (both DIR-825 and DWA-160). If I read correctly, both the router and network-adapter hardware is moving from Atheros to Ralink. It SOUNDS like Rev B DIR-825 allows Linux support, so it may have more of a future.
Dlink is not necessarily moving away from Atheros toward Ralink. Yes, the DWA160 Rev A was Atheros and the Rev B is Ralink but I don't quite understand why Dlink did that. It would have made more sense for the DWA160 Rev B to to be the Atheros 9002 chipset.
They should have created a new product with a Ralink chipset if they wanted one with same OEM as their new DIR-685.
I don't see a compelling reason to dump Atheros for Ralink. Atheros has a better complete solution, CPU and Radios, than just about any other vendor out there. When the true 3x3 450Mb/s radios are released we may see a change in the "leader" role but IMO right now its definitely not Ralink.