The basic question is "what's better for 1920x1080". Well, in my honest opionion (no fanboyism here) I'd recommend the Ati 4890, not only for it's increased performance, but also for it's amount of ram. It's only a little more then 100 MB over Nvidia's 260, but that might make the difference in more demanding games, like for example GTA IV.
And indeed, IF the price on the 275 drops, lets say below $250, then it's hard not to recommend that, seeing as quite a bit better then the 4890.