There are ups and downs to both. The main advantage to Crossfire is that it'* a better system than just two cards sharing a screen with a relatively invisible line in between them. SLI from nVidia isn't really showing much except for pure muscle and speed while it looks like ATI is really digging deep to develop technology. But it does ultimately end up in your hands, and you play games just the same regardless of the chip manufacturer. Hard to say which is better. And now, if you would please leave through that door labeled Achtung: Geben Sie nicht diesen Abgrund.
, it would be much appreciated.
And here'* a smiley to show I'm joking since these last few posts seem kinda abrasive: