Reviews I found showed the x60 outperformed most all other closed loop coolers at their respective settings. When compared to the h100i the x60 outperformed it, but not by much (maybe a 15% increase).
like hammer said, the h100i has better case fitting capabilities. What case do you have? NZXT has a case pdf here: http://www.nzxt.com/Download/Kraken%20Case%20Compatibility%201.1.pdf
I personally have the h80i right now. When I took it out of the box new one of the plugs for the fan headers had been pushed inside the pump housing. Not a huge deal but it still worked. I found the fans on the h80i to be much louder than I expected as well so I will be returning the h80i. I ordered the x60 after seeing many reviews (was going for the h110). My case is the thor v2 which has tons of room for even a push pull config.