Microsoft has backpedalled a bit with D365 only being in the cloud and are now offering an on premise version.
D365 is definitely the future for AX and would definitely be a good idea. Microsoft is heavily pushing the cloud model and support for AX 2009 is ending soon.
Not only that, but all of Microsoft’s significant resources are mainly being focused on D365 which means AX 2012 will slowly start receiving less and less love.
The logic will still be the same (currently) between AX 2012 and D365. However D365 projects will have much better toolsets and access to much better tools for less technical people.