Still, if all else equal, SLI>CF. However generally AMD>Nvidia for single GPU. So, if you are using a single display and DX11 games, AMD is my choice. For multiple display and older, DX9/10 games go nvidia, for now. AMD will fix frame pacing in those situations. The question is how long will they take? Hope this helps!
What about DX11 games Crossfire vs SLI? And if SLI is still better, by how much?
On one monitor? Its not significant. SLI has a bit better frame pacing, but it is basically fixed. To summarize, if all else is equal, go SLI, but I would not stop recommending CF if it was better value.