If you are interested in Bitcoin mining, the HD7990 is the only viable card of those three for that purpose. Otherwise, at least until possible driver fixes in July, FCAT testing has shown that Crossfire is [badly] broken, whereas SLI is not. SLI does not scale in every game though, so I would probably choose the Titan. For single monitor gaming, however, the cards I would suggest you consider are the HD7970 and the GTX670. Both are much cheaper than your selections. Once again, if you're also interested in Bitcoin mining, the HD7970 is the only rational choice of those two.