I think this one is pretty muched solved.
The NZXT Kraken x61 is THE best aio liquid cooler on the market currently.
I have had experience with both the h100i and kraken x61 and I prefer the x61 because of its cooling performance.
Idles with the Kraken were 10 degrees lower, at 25-29 while h100i was giving me 35-40 (occasionally 45).
I ruled out thermal paste application method when I reinstalled the cooler with Shin-Etsu. (temps dropped 3 degrees, but still worse than x61)
Loads were similar 60s for h100i, mid to low 50s for x61.
It boils down to the top coolers for all of the companies, it really doesn't matter which one you buy if you don't care about that extra 2 degrees, BUT if you DO care, go with the x61 because it has basically the biggest cooler out there with a dense fin design.
Cooler master nepton 28-L, Swifttech's Coolers, Corsair H110, h105, and NZXT's Kraken x61 are ALL good liquid coolers.
Thank you