I've used Ceramique for years because it's cheap, doesn't dry out, and has better temps than regular white grease provides. I did try switching to MX-2, and will admit that it gave a little boost to both air and water cooling (1-2C lower than Ceramique for me). Does this really validate the costs? I can snag a 20g tube of Ceramique for under $6...no way of that with MX-2.
The Shin-etsu X23 is good stuff, too, from what I've heard and seen in reviews. I have no experience with it. However, I do remember that AMD used a Shin-Etsu product between the CPU and heatspreader on A64 chips of yore, due to long-term stability.
Even white grease isn't bad if used properly, but it will dry out in a few months. The worst I've used in that regard was Zalman STG-1...dried out in 2 weeks or less, repeatedly, although temps were excellent while it was still wet. For now I'm sticking with MX-2, as I keep the giant Ceramique tube around for general builds.