In several rather well done tests of thermal compounds used in CPU/heatsink applications, the differences between the best and worst performers were minimal (a rather few degrees C). I suspect that JB Weld will perform as well as AA. And RTV will work as well as Fujik. Just keep the layer as thin as possible. Flexible stuff like RTV/Fujik tends to survive thermal cycling better than rigid stuff.
For potting and thermal adhesives I have used silicon carbide in epoxy or silicone rubber. It has MUCH better thermal conductivity that aluminum oxide. See: High Performance Potting Epoxy - Interested? for some discussion.
I have also used diamond dust in my thermal adhesives/greases. It is not very expensive and nothing conducts heat better. For the carrier in thermal greases I use high vacuum grease or oil.