Oh boy!! This could get ugly real fast...... we all have our own preference on which paste we use and recommend. I only use Shin Etsu Micro Si, but I'd say the prevailing choice for most would be Arctic Cooling MX-4 or AS5.
The PK-3 is OK but from the list I'd use Phobya Nano Grease.
Liquid ultra is probably the one you're thinking of as having an issue. But it won't with copper/nickel. It eats aluminium because of it's gallium content.
I use liquid ultra on that exact cpu, it's de dogs danglies
Not really that much difference between TIM, good brand ones anyway. The Liquid stuff is different though, you can get up to 5-10*c drop with that stuff. Only problem with it is it welds parts together and can damage the surfaces.
Well not literally weld together but it has a really strong bond and is hard to remove. Some of the older Liquid TIM was like that anyway, not sure about the newer stuff.