Neither. Both the 380 and the 960 are barely over a 1 step up, I have my old 660ti pulling benchmarks as high as the Gigabyte G1 960 gaming, which is one of the best performing 960's. I also have a gtx970 and it's a difference I can tell easily. I get over 60fps on dual monitors on all the games I play, set at ultra on the 660ti, but play those same games on the 970 and now it renders at 2k/4k drops down to 1080p and it's a whole different picture, not to mention the msaa, full physX, full shadows etc.
A good upgrade would be a r9 390 or gtx970 for a single gpu, but if you do plan on multiple cards, I'd stick with nvidia because to date the are still bugs with CF and many games still have poor CF optimization whereas sli doesn't seem to have the same amount of issues. I'd of think about amd CF if you plan on raising the resolution to 1440p multiple monitors and take advantage of AMD's greater ram.
Edit: forgot to mention that nvidia cards like the 970 are already set up to work with VR fully, I don't believe amd is.