It would not be wise to go Crossfire or SLI with that card. They are too weak and will just introduce microstuttering. SLI or CrossFire are meant for high end cards.
As for AMD vs Nvidia. Both have their advantages.
* Support for 4 displays (vs 2 for Nvidia)
* Lower power consumption
* Runs cooler
* Comes with a free game
* Supposedly better drivers
* Supports PhysX ( http://www.youtube.com/watch?v=EWFkDrKvBRU
* Supports FXAA/TXAA
* Supports Adaptive VSync
* Better 3D technology
* Supports old motherboards with PCIe 1.0
If I missed something, others please correct me