As you said above, GTX 660 is a better choice if you will SLI.
SLI is been always more Hassle free than Crossfire. Crossfire has many issues like stutters and Driver problems.
I have a GTX 660 and it maxes every game at good fps in 1080p.
A 3x way SLI is pretty Overkill for 1080p and a Tough Contender for Triple Monitor setup.
I would recommend you 2x660 setup. It will give you enough power to max every game at 1080p at a constant 60+ fps.
If you are Confused between brands, Get the MSI GTX 660 Twin Frozr III
It a very good Card with Super Cooling and it Overclocks way nicely.