The GTX 560Ti is better(asus). If going Radeon, then it should be the HD 6950 1GB.
I Agree, the 560TI is better than the 6870, but if you can go for the 6950 1GB cards.
The 560ti does support 3d,but need to SLI to make it worth it and an expensive 3D screen.
I got a 6950 1GB (ASUS DCii) and loved it, so I got another one and no need to upgrade for atleast two years.