I vote for ceramique. Any test I've seen has shown it to be *at least* as good as AS5, and some have shown it to be better. On top of that, AFAIK, it's not electrically conductive, which is always a plus. I use it on my rig.
i like ceramique as well. works great for me. i don't know of any issues with watercooling and compounds, so any one should work just as well as on aircooling, but i recommend ceramique.
Arctic Silver 5 is better than Ceramique, it just takes 200 hours to get the best results.
The only time you will see a review showing ceramique to be better is when the reviewer didn't allow for the product to achieve maximum particle to particle thermal conduction and for the heatsink to CPU interface to reach maximum conductivity. This takes several thermal cycles and up to 200 hours or more.
Once the break in period is over the temps should drop 2*-5*celcius.
Ceramique is a good product but Arctic Silver 5 is better.