If you want the best with insane price level, buy into Power/AIX. If you are not really sure, please don't. You need to train administrators (with larger setups) - or prepare to shell in a lot of money, the hardware contains nasty licensing surprises, the hardware is rather expensive, and so on. When you get it running, it's insanely powerful indeed, and the platform itself nearly never screws up (if you tested properly for Monday parts), and the virtualization is insanely good in practice.
Some potential customers have bought Power/AIX, some not. The ones that did are still years after customers, and to my knowledge pretty happy. I believe IBM is actually gaining customers. Slowly, but they are. Those that made the choice knew what they got into, and are not going to change their views.
This is my experience as well. IMO, Power/AIX has the most sophisticated virtualization available. IBM just has no idea how to market it.
I was talking to an ibmer a while ago and AIX was mentioned. We agreed the platform had technical merits, and on a pure platform level was superior to x32/x64 but the network effects of commodity hardware had already won the platform game. No one writes software for any other platforms but intel/amd64. AIX lost for the battle, similar to the reasons betamax lost to VHS.