Although I am water-cooling, I went with PK-1 for mounting my Apogee HD White to my 3930K, and I couldn't be more pleased with it. I am also using it between my GTX670FTW GPU and Heatkiller GPU^X3 680 Hole Edition Waterblock with fantastic results.
I have used AS5, IC Diamond, Antec Formula7, AS Ceramique, Swiftech's no-name-mentioned TIM, MX2/3/4, Tuniq TX4, Noctua NH1, Phobya HEGrease, Gelid GC-Extreme, all variants of Shin-Etsu (which range from absolutely awful to very good), and probably at least a dozen others.
Compared to all of the above, the PK1 is my absolute favorite TIM and its performance is extremely consistent. I do my best to use the absolute smallest amount of TIM possible, literally just enough to fill in any gaps (slightly more if there is a convex/concave IHS or HSF/Block surface), and the PK1 was worth 6.2C over Ceramique under P95. It is a moderately-thick paste which is what I personally prefer, but unlike some others with similar viscosity, it is extremely easy to use and to remove. Also, it is the only TIM I have used which seems to not care at all about application pattern; I have done an "X", single dot, four dots, straight lines either vertical or horizontal (single and double lines), and I have applied a small amount to both the IHS and Block Base and then used a business card to scrape off the vast majority on each leaving just the bits that managed to find the crevices on each. Every single method performs within 0.5C of the other, with the last method performing the best (although I lapped my Apogee HD to perfect flatness and up through 6000grit automotive wet-sanding sandpaper; prior to lapping, the cold plate was very poorly finished and the last method of application was worth a good 2.5C over anything else due to the many surface scratches).
CoolLaboratory Liquid Pro/Ult are both amazing liquid metal TIM's, but application is a PITA (Indigo-X is even better but too expensive for how often I remount) and there is a serious concern about its electrical conductivity.
In the end, $8 or so for a 7Gram tube of PK1 is a steal!