Like KaHNZa said the bigger the better. Larger fans don't need to spin as fast to shift the same amount of air, as they spin slower they are quieter, which is good if you've tried a delta before!!
Note on blow hole installation:
Don't make the same mistake I did! Make sure that when you've put the fan inside the case the whole thing will go back together. I stripped my case out, put an 80mm fan in the top, then found the Power supply wouldn't fit back in. Ooops! Measure and measure again. Then check once more!