HD 7850 Hands Down.
Vs. 570, its like 5% behind at stock speeds, but when overclocked it easily reaces 7870 speeds, which are much faster than 570 speeds. And 7850 runs way cooler and quieter than a 570, and consumes less power, all due to the new 28nm manufacturing process.
No other card really matches if you're looking for 250$ card..
Maybe you can wait for the 660 series, I don't know how far away they are from release but if they're close, I would.