what looney bin u crawl out of. if you answer his question on his merits the 6870 has higher values across the board than the 560 YET they perform very close to the same. and depending on game played or application he will be using is a far better way to determine which card he goes with. just using the 6870/560 as examples here
whatever looney bin i crawled out of is one you need to visit. your example is a very poor on indeed since the 6870 and 560 are very similar in rendering, clock speed, memory bandwidth and texture fill rate:http://www.hwcompare.com/11005/geforce-gtx-560-vs-radeon-hd-6870/
or it is no surprise they would perform similarly.
the OP is asking an objective question:"what makes a good GPU" not "what is a good GPU for game (x) or application (x)."
so if you cannot do more than jump on someone's bandwagon by agreeing or criticizing an answer you have no idea about; you need to sit back, STFU and learn something.