7800 series release on the 19th, and TH already has a review article on benchmarks from the paper release, so you can get a really good feel of how they'll preform. I'm the current owner of a 7950 and I can tell you that while it preforms and OCs like a champ, AMD drivers does have its problems.
My recommendation would depend on what you're willing to put up with. if you have the standard 20-27" 1080p monitor, the 560ti with its very mature drivers etc should serve you well. the 7870 will preform way better than a 560ti, but you'll get the occasional weird crash out of the blue until they fix up the drivers. of course, if you ever plan on getting a 2nd card in the future for some 3-4 monitor eyefinity craziness, get the 7870, it'll have better availability a year down the road.